# Glossary > 360 technical terms ## HTTP Concepts - [Idempotency](https://statuscodefyi.com/glossary/idempotency/): A property of HTTP methods where making the same request multiple times produces the same result as making it once. GET,... - [Safe Methods](https://statuscodefyi.com/glossary/safe-methods/): HTTP methods that do not modify server state. GET, HEAD, OPTIONS, and TRACE are considered safe methods. Browsers, crawl... - [Content Negotiation](https://statuscodefyi.com/glossary/content-negotiation/): The mechanism by which a client and server agree on the best representation of a resource. The client sends Accept, Acce... - [Status Code](https://statuscodefyi.com/glossary/status-code/): A three-digit numeric code in an HTTP response that indicates the outcome of a request. Status codes are grouped into fi... - [Reason Phrase](https://statuscodefyi.com/glossary/reason-phrase/): A short textual description that accompanies an HTTP status code in the response status line, such as 'Not Found' for 40... - [Media Type (MIME Type)](https://statuscodefyi.com/glossary/media-type/): A standardized identifier for the format of data transmitted over the internet. Media types follow the pattern type/subt... - [Response Header](https://statuscodefyi.com/glossary/response-header/): Metadata fields sent by the server as part of an HTTP response. Response headers provide information about the server, t... - [Request Method (HTTP Verb)](https://statuscodefyi.com/glossary/request-method/): The action a client wants to perform on a resource, specified in the request line. Standard HTTP methods include GET (re... - [Redirect](https://statuscodefyi.com/glossary/redirect/): An HTTP mechanism where the server instructs the client to request a different URL. Redirects use 3xx status codes: 301 ... - [Cookie](https://statuscodefyi.com/glossary/cookie/): A small piece of data stored by the browser and sent back to the server with every subsequent request. Cookies are set v... - [Session](https://statuscodefyi.com/glossary/session/): A server-side mechanism for maintaining state across multiple HTTP requests from the same client. Since HTTP is stateles... - [HTTP/2](https://statuscodefyi.com/glossary/http2/): The second major version of the HTTP protocol, standardized in RFC 7540. HTTP/2 introduced binary framing, multiplexing,... - [HTTP/3](https://statuscodefyi.com/glossary/http3/): The third major version of HTTP, standardized in RFC 9114, built on QUIC instead of TCP. QUIC provides built-in encrypti... - [REST (Representational State Transfer)](https://statuscodefyi.com/glossary/rest/): An architectural style for designing networked applications. RESTful APIs use standard HTTP methods (GET, POST, PUT, DEL... - [GraphQL](https://statuscodefyi.com/glossary/graphql/): A query language and runtime for APIs developed by Facebook. Unlike REST, which exposes multiple endpoints, GraphQL uses... - [Keep-Alive](https://statuscodefyi.com/glossary/keep-alive/): A mechanism that reuses a single TCP connection for multiple HTTP requests, reducing latency by avoiding repeated TCP ha... - [Chunked Transfer Encoding](https://statuscodefyi.com/glossary/chunked-transfer/): An HTTP transfer mechanism where data is sent in chunks, allowing streaming responses without knowing the total content ... - [Conditional Request](https://statuscodefyi.com/glossary/conditional-request/): An HTTP request that includes conditions (If-Match, If-None-Match, If-Modified-Since) allowing the server to respond wit... - [Range Request](https://statuscodefyi.com/glossary/range-request/): An HTTP mechanism allowing clients to request only a portion of a resource using the Range header, enabling resumable do... - [Trailer Headers](https://statuscodefyi.com/glossary/trailer-headers/): HTTP headers sent after the message body in chunked transfer encoding, useful for checksums or digital signatures comput... ## API Design - [Rate Limiting](https://statuscodefyi.com/glossary/rate-limiting/): A technique to control the number of API requests a client can make within a time window, preventing abuse and ensuring ... - [Pagination](https://statuscodefyi.com/glossary/pagination/): A pattern for dividing large datasets into discrete pages, using cursor-based or offset-based approaches to efficiently ... - [API Versioning](https://statuscodefyi.com/glossary/api-versioning/): Strategies for maintaining backward compatibility when evolving APIs, including URL path versioning (/v1/), header versi... - [Content-Type](https://statuscodefyi.com/glossary/content-type/): An HTTP header indicating the media type of the request or response body (e.g., application/json, text/html), essential ... - [Accept Header](https://statuscodefyi.com/glossary/accept-header/): An HTTP request header that specifies which media types the client can process, enabling server-driven content negotiati... - [HATEOAS](https://statuscodefyi.com/glossary/hateoas/): Hypermedia As The Engine Of Application State — a REST constraint where API responses include links to related resources... - [Idempotency Key](https://statuscodefyi.com/glossary/idempotency-key/): A unique identifier sent with API requests to ensure that retried requests don't create duplicate side effects, commonly... - [Webhook](https://statuscodefyi.com/glossary/webhook/): A user-defined HTTP callback triggered by an event in a source system, pushing real-time notifications to a specified UR... - [API Gateway](https://statuscodefyi.com/glossary/api-gateway/): A server that acts as a single entry point for API requests, handling routing, rate limiting, authentication, and load b... - [OpenAPI Specification](https://statuscodefyi.com/glossary/openapi/): A standard format (formerly Swagger) for describing RESTful APIs, including endpoints, request/response schemas, authent... - [GraphQL Query](https://statuscodefyi.com/glossary/graphql-query/): A read operation in GraphQL that allows clients to request exactly the data fields they need in a single request, avoidi... - [REST Constraints](https://statuscodefyi.com/glossary/rest-constraints/): The six architectural constraints that define REST: client-server, stateless, cacheable, uniform interface, layered syst... - [API Throttling](https://statuscodefyi.com/glossary/api-throttling/): A mechanism that limits the processing rate of API requests, queuing or rejecting excess requests to protect backend ser... - [Request Body](https://statuscodefyi.com/glossary/request-body/): The data payload sent with HTTP requests (typically POST, PUT, PATCH), containing the resource representation to be crea... - [Response Body](https://statuscodefyi.com/glossary/response-body/): The data payload returned by the server in an HTTP response, containing the requested resource, error details, or action... - [SDK (Software Development Kit)](https://statuscodefyi.com/glossary/sdk/): A collection of libraries, tools, and documentation that simplifies integration with an API or protocol in a specific pr... - [API Deprecation](https://statuscodefyi.com/glossary/api-deprecation/): The process of marking an API version or endpoint as obsolete, giving consumers a sunset date to migrate before the endp... - [Bulk Operations](https://statuscodefyi.com/glossary/bulk-operations/): An API pattern for creating, updating, or deleting multiple resources in a single request to reduce HTTP round trips. A ... - [Hypermedia](https://statuscodefyi.com/glossary/hypermedia/): The principle of embedding links and controls within API responses so clients discover available actions dynamically rat... - [JSON:API](https://statuscodefyi.com/glossary/json-api/): A specification for building JSON APIs that standardizes resource structure, relationships, pagination, and error format... ## Security - [TLS Handshake](https://statuscodefyi.com/glossary/tls-handshake/): The process by which a client and server establish a secure, encrypted connection. During the handshake, they negotiate ... - [TLS Certificate (SSL Certificate)](https://statuscodefyi.com/glossary/certificate/): A digital document that verifies the identity of a website and enables encrypted connections. Certificates are issued by... - [CORS (Cross-Origin Resource Sharing)](https://statuscodefyi.com/glossary/cors/): A browser security mechanism that controls which domains can make requests to a server. By default, browsers block cross... - [Cipher Suite](https://statuscodefyi.com/glossary/cipher-suite/): A named combination of cryptographic algorithms used in a TLS connection. A cipher suite specifies the key exchange algo... - [Authentication](https://statuscodefyi.com/glossary/authentication/): The process of verifying the identity of a client or user. HTTP supports multiple authentication schemes: Basic (base64 ... - [XSS (Cross-Site Scripting)](https://statuscodefyi.com/glossary/xss/): A security vulnerability where attackers inject malicious scripts into web pages viewed by other users. Stored XSS persi... - [CSRF (Cross-Site Request Forgery)](https://statuscodefyi.com/glossary/csrf-attack/): An attack that tricks a user's browser into making unintended requests to a website where the user is authenticated. The... - [SQL Injection](https://statuscodefyi.com/glossary/sql-injection/): A code injection attack that exploits vulnerabilities in database query construction. Attackers insert malicious SQL cod... - [HSTS (HTTP Strict Transport Security)](https://statuscodefyi.com/glossary/hsts/): A security policy mechanism that forces browsers to only connect to a website over HTTPS. The server sends a Strict-Tran... - [CSP (Content Security Policy)](https://statuscodefyi.com/glossary/csp/): An HTTP security header that controls which resources a browser is allowed to load for a given page. CSP mitigates XSS a... - [OAuth 2.0](https://statuscodefyi.com/glossary/oauth/): An authorization framework that enables third-party applications to access a user's resources without exposing their cre... - [JWT (JSON Web Token)](https://statuscodefyi.com/glossary/jwt/): A compact, URL-safe token format for securely transmitting claims between parties. A JWT consists of three Base64URL-enc... - [API Key](https://statuscodefyi.com/glossary/api-key/): A unique identifier used to authenticate API requests, typically passed as a header or query parameter, simpler than OAu... - [Bearer Token](https://statuscodefyi.com/glossary/bearer-token/): An opaque access token sent in the Authorization header (Bearer scheme) that grants the holder access to protected resou... - [Mutual TLS (mTLS)](https://statuscodefyi.com/glossary/mutual-tls/): A TLS authentication mode where both client and server present certificates, providing bidirectional identity verificati... - [Rate Limit Bypass](https://statuscodefyi.com/glossary/rate-limit-bypass/): Techniques attackers use to circumvent rate limiting, including IP rotation, header manipulation, and distributed reques... - [Same-Origin Policy](https://statuscodefyi.com/glossary/same-origin-policy/): A browser security mechanism that restricts scripts from one origin from accessing resources of another origin, forming ... - [Clickjacking](https://statuscodefyi.com/glossary/clickjacking/): An attack that tricks users into clicking hidden elements by overlaying a transparent iframe over a legitimate page, cau... - [SSRF (Server-Side Request Forgery)](https://statuscodefyi.com/glossary/ssrf/): An attack where an attacker manipulates a server into issuing HTTP requests to internal resources — such as cloud metada... - [Security Headers](https://statuscodefyi.com/glossary/security-headers/): A collection of HTTP response headers that harden web application security by instructing browsers how to behave when ha... ## Networking - [TCP/IP](https://statuscodefyi.com/glossary/tcp-ip/): The foundational protocol suite of the internet. TCP (Transmission Control Protocol) provides reliable, ordered delivery... - [Three-Way Handshake](https://statuscodefyi.com/glossary/three-way-handshake/): The process used to establish a TCP connection between client and server. The client sends a SYN packet, the server resp... - [Port Number](https://statuscodefyi.com/glossary/port/): A 16-bit number (0-65535) that identifies a specific service or process on a networked host. Well-known ports include 80... - [Latency](https://statuscodefyi.com/glossary/latency/): The time delay between sending a request and receiving a response. Network latency is measured in milliseconds and affec... - [Timeout](https://statuscodefyi.com/glossary/timeout/): A limit on how long a client or server will wait for a response before giving up. Connection timeouts occur when a TCP c... - [Load Balancer](https://statuscodefyi.com/glossary/load-balancer/): A device or software that distributes incoming network traffic across multiple backend servers. Load balancers improve a... - [Reverse Proxy](https://statuscodefyi.com/glossary/reverse-proxy/): A server that sits between clients and backend servers, forwarding client requests and returning server responses. Rever... - [NAT (Network Address Translation)](https://statuscodefyi.com/glossary/nat/): A technique that maps private IP addresses to a public IP address, allowing multiple devices on a local network to share... - [Firewall](https://statuscodefyi.com/glossary/firewall/): A network security system that monitors and controls incoming and outgoing traffic based on predetermined rules. Firewal... - [Proxy Server (Forward Proxy)](https://statuscodefyi.com/glossary/proxy-server/): An intermediary server that sits between a client and the internet, forwarding client requests on their behalf. Forward ... - [DNS over HTTPS (DoH)](https://statuscodefyi.com/glossary/dns-over-https/): A protocol for performing DNS resolution via the HTTPS protocol. DoH encrypts DNS queries and responses, preventing eave... - [IPv6](https://statuscodefyi.com/glossary/ipv6/): The latest version of the Internet Protocol, designed to replace IPv4. IPv6 uses 128-bit addresses (e.g., 2001:0db8::1) ... - [Subnet (Subnetwork)](https://statuscodefyi.com/glossary/subnet/): A logical subdivision of an IP network created by dividing the IP address into network and host portions using a subnet ... - [Connection Pooling](https://statuscodefyi.com/glossary/connection-pooling/): Reusing existing network connections instead of creating new ones for each request, significantly reducing latency and r... - [TCP Reset (RST)](https://statuscodefyi.com/glossary/tcp-reset/): A TCP segment that abruptly terminates a connection without the normal four-way handshake, often caused by firewalls, po... - [MTU (Maximum Transmission Unit)](https://statuscodefyi.com/glossary/mtu/): The largest packet size that can be transmitted over a network link without fragmentation, typically 1500 bytes for Ethe... - [Socket](https://statuscodefyi.com/glossary/socket/): A software endpoint for bidirectional network communication, identified by an IP address and port number, forming the fo... - [UDP (User Datagram Protocol)](https://statuscodefyi.com/glossary/udp/): A connectionless transport protocol that sends discrete datagrams without establishing a session, guaranteeing neither o... - [Bandwidth](https://statuscodefyi.com/glossary/bandwidth/): The maximum rate of data transfer across a network path, measured in bits per second (bps, Mbps, Gbps). Bandwidth is the... - [DNS Lookup](https://statuscodefyi.com/glossary/dns-lookup/): The process of querying DNS servers to translate a hostname into an IP address before a TCP connection can be establishe... ## Caching & Performance - [Cache-Control](https://statuscodefyi.com/glossary/cache-control/): An HTTP header that specifies caching directives for requests and responses. Common directives include max-age (seconds ... - [ETag (Entity Tag)](https://statuscodefyi.com/glossary/etag/): An HTTP response header that provides a unique identifier for a specific version of a resource. Clients can send the ETa... - [CDN (Content Delivery Network)](https://statuscodefyi.com/glossary/cdn/): A globally distributed network of servers that caches and delivers content from locations geographically close to users.... - [Stale-While-Revalidate](https://statuscodefyi.com/glossary/stale-while-revalidate/): A Cache-Control extension directive (defined in RFC 5861) that allows a cache to serve a stale response while asynchrono... - [Cache Invalidation](https://statuscodefyi.com/glossary/cache-invalidation/): The process of removing or marking cached data as stale when the underlying content changes. Cache invalidation is notor... - [Edge Caching](https://statuscodefyi.com/glossary/edge-caching/): The practice of storing cached content at edge servers located geographically close to end users, rather than at the ori... - [Last-Modified](https://statuscodefyi.com/glossary/last-modified/): An HTTP response header indicating when the resource was last changed, used with If-Modified-Since for conditional reque... - [Vary Header](https://statuscodefyi.com/glossary/vary-header/): An HTTP response header that tells caches which request headers affect the response, ensuring that different versions of... - [Cache Busting](https://statuscodefyi.com/glossary/cache-busting/): Techniques for forcing browsers and CDNs to fetch fresh content by changing URLs (adding query strings, content hashes, ... - [HTTP Compression](https://statuscodefyi.com/glossary/http-compression/): Reducing response size using algorithms like gzip, Brotli, or zstd, configured via Accept-Encoding and Content-Encoding ... - [Prefetching](https://statuscodefyi.com/glossary/prefetch/): A browser optimization that proactively fetches resources likely needed for future navigations, using link rel="prefetch... - [Time to First Byte (TTFB)](https://statuscodefyi.com/glossary/ttfb/): The time between sending an HTTP request and receiving the first byte of the response, a key performance metric indicati... - [Connection Reuse](https://statuscodefyi.com/glossary/connection-reuse/): Sending multiple HTTP requests over a single TCP connection (HTTP/1.1 keep-alive or HTTP/2 multiplexing) to avoid the ov... - [Brotli Compression](https://statuscodefyi.com/glossary/brotli/): A modern lossless compression algorithm developed by Google that achieves 15–25% better compression ratios than gzip for... - [HTTP Caching Layers](https://statuscodefyi.com/glossary/http-caching-layers/): The hierarchy of caches a response passes through between the origin server and the end user's browser. Layers include t... - [Cache Hit Ratio](https://statuscodefyi.com/glossary/cache-hit-ratio/): The percentage of requests served directly from cache without contacting the origin server, expressed as hits / (hits + ... - [Push Cache (HTTP/2)](https://statuscodefyi.com/glossary/push-cache/): The least-persistent caching layer in HTTP/2, storing server-pushed resources only for the lifetime of a single HTTP/2 c... - [Immutable Response](https://statuscodefyi.com/glossary/immutable-response/): A Cache-Control extension (Cache-Control: immutable) that tells browsers the response body will never change for the dur... - [Service Worker Cache](https://statuscodefyi.com/glossary/service-worker-cache/): A programmable JavaScript cache layer that runs in the browser background and intercepts network requests via fetch even... - [103 Early Hints](https://statuscodefyi.com/glossary/103-early-hints/): An informational HTTP status code that allows the server to send preliminary Link response headers before the final resp... ## Error Handling - [Retry Strategy](https://statuscodefyi.com/glossary/retry-strategy/): A pattern for automatically retrying failed requests with techniques like exponential backoff, jitter, and maximum retry... - [Circuit Breaker](https://statuscodefyi.com/glossary/circuit-breaker/): A resilience pattern that prevents cascading failures by stopping requests to a failing service after a threshold of err... - [Graceful Degradation](https://statuscodefyi.com/glossary/graceful-degradation/): A design approach where a system continues operating with reduced functionality when components fail, rather than failin... - [Fallback](https://statuscodefyi.com/glossary/fallback/): An alternative response or behavior used when the primary service or resource is unavailable, such as serving cached dat... - [Error Boundary](https://statuscodefyi.com/glossary/error-boundary/): A mechanism for catching and handling errors at a specific level in a system, preventing unhandled errors from propagati... - [Dead Letter Queue](https://statuscodefyi.com/glossary/dead-letter-queue/): A queue where messages that cannot be processed are stored for later analysis, commonly used in asynchronous systems to ... - [Health Check](https://statuscodefyi.com/glossary/health-check/): An endpoint or mechanism that reports the operational status of a service, used by load balancers and orchestrators to r... - [Timeout Budget](https://statuscodefyi.com/glossary/timeout-budget/): A pattern where the total time allowed for a request is divided among sub-operations, ensuring that no single step can e... - [Backpressure](https://statuscodefyi.com/glossary/backpressure/): A flow control mechanism where a consumer signals to a producer to slow down when it cannot keep up with the rate of inc... - [Problem Details (RFC 9457)](https://statuscodefyi.com/glossary/problem-details/): A standardized JSON format for representing HTTP API errors, including type, title, status, detail, and instance fields ... - [Exponential Backoff](https://statuscodefyi.com/glossary/exponential-backoff/): A retry timing strategy where the wait interval doubles after each consecutive failure — for example, 1 s, 2 s, 4 s, 8 s... - [Jitter](https://statuscodefyi.com/glossary/jitter/): Random variation added to retry delays to prevent multiple clients from retrying simultaneously after a shared failure e... - [Thundering Herd](https://statuscodefyi.com/glossary/thundering-herd/): A problem where a large number of clients simultaneously retry or reconnect after a shared failure, overwhelming the ser... - [Bulkhead Pattern](https://statuscodefyi.com/glossary/bulkhead-pattern/): A resilience pattern borrowed from ship design that partitions system resources — thread pools, connection pools, semaph... - [Error Code Mapping](https://statuscodefyi.com/glossary/error-code-mapping/): The practice of translating internal application error codes or exception types to the appropriate protocol-level status... - [Idempotent Retry](https://statuscodefyi.com/glossary/idempotent-retry/): The practice of safely retrying a failed request because the underlying operation is idempotent — producing the same res... - [Error Rate](https://statuscodefyi.com/glossary/error-rate/): The percentage of requests that result in error responses (HTTP 4xx or 5xx, gRPC non-OK status) over a given time window... - [Poison Message](https://statuscodefyi.com/glossary/poison-message/): A message in a queue that repeatedly causes processing failures, blocking forward progress and consuming retry budget. P... - [Fail Open / Fail Closed](https://statuscodefyi.com/glossary/fail-open-fail-closed/): Two opposing failure modes for a system check or gate. Fail open allows requests through when the check itself is unavai... - [Retry-After Header](https://statuscodefyi.com/glossary/retry-after-header/): An HTTP response header that tells the client how long to wait before issuing another request. It is sent with 429 Too M... ## Protocol Design - [Request-Response Model](https://statuscodefyi.com/glossary/request-response/): A communication pattern where a client sends a request and waits for a server to send back a response. HTTP, SMTP, FTP, ... - [RFC (Request for Comments)](https://statuscodefyi.com/glossary/rfc/): A formal document published by the IETF (Internet Engineering Task Force) that defines internet standards, protocols, an... - [IANA (Internet Assigned Numbers Authority)](https://statuscodefyi.com/glossary/iana/): The organization responsible for maintaining global registries of internet protocol parameters, including HTTP status co... - [Protocol Upgrade](https://statuscodefyi.com/glossary/protocol-upgrade/): The process of switching from one protocol to another over an existing connection. HTTP/1.1's Upgrade header enables swi... - [Multiplexing](https://statuscodefyi.com/glossary/multiplexing/): The ability to send multiple requests and responses simultaneously over a single connection. HTTP/2 introduced multiplex... - [Backward Compatibility](https://statuscodefyi.com/glossary/backward-compatibility/): The ability of a newer version of a protocol or system to work with older versions without breaking existing functionali... - [Protocol Buffers (Protobuf)](https://statuscodefyi.com/glossary/protocol-buffer/): A language-neutral, platform-neutral binary serialization format developed by Google. Protocol Buffers define message sc... - [Serialization](https://statuscodefyi.com/glossary/serialization/): The process of converting structured data into a format suitable for transmission or storage. Common serialization forma... - [Protocol Negotiation](https://statuscodefyi.com/glossary/protocol-negotiation/): The process by which client and server agree on which protocol version or features to use for communication, such as ALP... - [Message Framing](https://statuscodefyi.com/glossary/message-framing/): The method of delimiting individual messages within a stream of bytes, using techniques like length-prefixed frames (gRP... - [Wire Format](https://statuscodefyi.com/glossary/wire-format/): The exact byte-level representation of data as transmitted over the network, including encoding, byte ordering, and fiel... - [Extension Mechanism](https://statuscodefyi.com/glossary/extension-mechanism/): A protocol feature that allows adding new capabilities without breaking existing implementations, such as HTTP headers, ... - [Connection-Oriented](https://statuscodefyi.com/glossary/connection-oriented/): A communication model that requires establishing a persistent logical connection between sender and receiver before any ... - [Connectionless](https://statuscodefyi.com/glossary/connectionless/): A communication model that sends self-contained datagrams without establishing a prior connection or maintaining shared ... - [Half-Duplex](https://statuscodefyi.com/glossary/half-duplex/): A communication mode where data can flow in both directions between two endpoints, but only in one direction at a time. ... - [Full-Duplex](https://statuscodefyi.com/glossary/full-duplex/): A communication mode where data flows simultaneously in both directions between two endpoints without taking turns. WebS... - [ALPN (Application-Layer Protocol Negotiation)](https://statuscodefyi.com/glossary/alpn/): A TLS extension (RFC 7301) that allows the client and server to negotiate which application protocol they will use durin... - [Text vs Binary Protocol](https://statuscodefyi.com/glossary/text-vs-binary-protocol/): The distinction between protocols that encode messages as human-readable ASCII or UTF-8 text versus those that encode me... - [Head-of-Line Blocking](https://statuscodefyi.com/glossary/head-of-line-blocking/): A performance problem where a slow or lost packet blocks the processing of all subsequent packets in the same ordered st... - [QUIC](https://statuscodefyi.com/glossary/quic/): A UDP-based transport protocol developed by Google and standardized in RFC 9000 that combines TLS 1.3 encryption with mu... ## DNS - [DNS Resolution](https://statuscodefyi.com/glossary/dns-resolution/): The process of translating a human-readable domain name (like example.com) into an IP address. DNS resolution involves r... - [DNS Record Types](https://statuscodefyi.com/glossary/dns-record-types/): Different categories of data stored in the Domain Name System. Common types include A (IPv4 address), AAAA (IPv6 address... - [TTL (Time to Live)](https://statuscodefyi.com/glossary/ttl/): In DNS, the duration in seconds that a DNS record can be cached by resolvers before they must re-query the authoritative... - [DNSSEC (DNS Security Extensions)](https://statuscodefyi.com/glossary/dnssec/): A suite of extensions to DNS that adds cryptographic authentication to DNS responses. DNSSEC uses digital signatures to ... - [DNS over TLS (DoT)](https://statuscodefyi.com/glossary/dns-over-tls/): A protocol for encrypting DNS queries using TLS on a dedicated port (853). Unlike DNS over HTTPS, which uses port 443 an... - [Anycast](https://statuscodefyi.com/glossary/anycast/): A network addressing method where the same IP address is announced from multiple locations worldwide. Routers direct tra... - [Recursive Resolver](https://statuscodefyi.com/glossary/recursive-resolver/): A DNS server that performs the full resolution process on behalf of the client, querying root, TLD, and authoritative na... - [Authoritative Name Server](https://statuscodefyi.com/glossary/authoritative-nameserver/): A DNS server that holds the actual DNS records for a domain and provides definitive answers, as opposed to recursive res... - [Glue Record](https://statuscodefyi.com/glossary/glue-record/): An A or AAAA record provided by a parent zone to break circular dependencies when a name server's hostname is within the... - [EDNS(0)](https://statuscodefyi.com/glossary/edns/): Extension Mechanisms for DNS — a backward-compatible extension that allows larger UDP messages, additional flags, and op... - [DNS Zone](https://statuscodefyi.com/glossary/dns-zone/): A portion of the DNS namespace managed by a specific organization, defined by a zone file containing all records for tha... - [DNS Propagation](https://statuscodefyi.com/glossary/dns-propagation/): The time it takes for DNS record changes to spread across all recursive resolvers worldwide, typically governed by TTL v... - [CNAME Record](https://statuscodefyi.com/glossary/cname-record/): A DNS record that maps an alias domain name to a canonical (true) domain name, creating a redirect at the DNS level. Res... - [MX Record](https://statuscodefyi.com/glossary/mx-record/): A DNS record specifying the mail server responsible for receiving email for a domain, with priority values for failover ... - [SRV Record](https://statuscodefyi.com/glossary/srv-record/): A DNS record that specifies the hostname, port, priority, and weight for a specific service, used by SIP, XMPP, and serv... - [PTR Record](https://statuscodefyi.com/glossary/ptr-record/): A DNS record that maps an IP address to a domain name (reverse DNS), stored under the in-addr.arpa or ip6.arpa zones. PT... - [DNS Cache Poisoning](https://statuscodefyi.com/glossary/dns-cache-poisoning/): An attack that injects forged DNS records into a resolver's cache, redirecting users to malicious servers without their ... - [DNS Root Server](https://statuscodefyi.com/glossary/root-server/): One of 13 root server clusters (A through M) that form the top of the DNS hierarchy and direct queries to TLD nameserver... - [Split-Horizon DNS](https://statuscodefyi.com/glossary/split-horizon-dns/): A DNS configuration that returns different answers based on the source of the query, typically used to serve internal IP... - [Wildcard DNS Record](https://statuscodefyi.com/glossary/wildcard-dns/): A DNS record using an asterisk (*) that matches any subdomain not explicitly defined, commonly used for catch-all routin... ## Email & SMTP - [SMTP Relay](https://statuscodefyi.com/glossary/smtp-relay/): The process of forwarding email from one SMTP server to another. When you send an email, your mail client submits it to ... - [SPF, DKIM, and DMARC](https://statuscodefyi.com/glossary/spf-dkim-dmarc/): Three email authentication standards that prevent spoofing and phishing. SPF (Sender Policy Framework) specifies which s... - [Bounce Rate (Email)](https://statuscodefyi.com/glossary/bounce-rate/): The percentage of sent emails that are returned undelivered. Hard bounces indicate permanent delivery failures (e.g., SM... - [Email Deliverability](https://statuscodefyi.com/glossary/email-deliverability/): The ability of an email to reach the recipient's inbox rather than being blocked, bounced, or filtered to spam. Delivera... - [MTA (Mail Transfer Agent)](https://statuscodefyi.com/glossary/mta/): Software responsible for transferring email messages between servers using SMTP. An MTA receives email from a mail clien... - [SMTP Pipelining](https://statuscodefyi.com/glossary/smtp-pipeline/): An SMTP extension (ESMTP PIPELINING) that allows sending multiple commands without waiting for each response, improving ... - [Greylisting](https://statuscodefyi.com/glossary/greylisting/): An anti-spam technique where the mail server temporarily rejects email from unknown senders with a 4xx code, expecting l... - [Backscatter](https://statuscodefyi.com/glossary/backscatter/): Misdirected bounce messages sent to forged sender addresses, a form of spam caused by accepting then bouncing messages w... - [Envelope vs Header](https://statuscodefyi.com/glossary/envelope-vs-header/): The distinction between SMTP envelope addresses (MAIL FROM/RCPT TO) used for routing, and email headers (From/To) displa... - [STARTTLS](https://statuscodefyi.com/glossary/starttls/): An SMTP extension that upgrades an existing plaintext connection to encrypted TLS, different from implicit TLS which sta... - [SMTP Authentication (SMTP AUTH)](https://statuscodefyi.com/glossary/smtp-auth/): An SMTP extension (RFC 4954) requiring clients to authenticate with credentials before the server will relay their messa... - [Open Relay](https://statuscodefyi.com/glossary/open-relay/): An SMTP server that forwards email from any sender to any recipient without authentication, commonly exploited by spamme... - [Email Queue](https://statuscodefyi.com/glossary/email-queue/): A temporary storage mechanism where the MTA holds outbound messages for delivery, retrying on temporary failures indicat... - [MIME Multipart](https://statuscodefyi.com/glossary/mime-multipart/): The format for email messages containing multiple content types (text, HTML, attachments) using boundary-delimited parts... - [ARC (Authenticated Received Chain)](https://statuscodefyi.com/glossary/arc/): An email authentication protocol (RFC 8617) that preserves SPF, DKIM, and DMARC validation results across forwarding hop... - [BIMI (Brand Indicators for Message Identification)](https://statuscodefyi.com/glossary/bimi/): An email standard that displays a brand's verified logo next to authenticated messages in the recipient's inbox, requiri... - [DSN (Delivery Status Notification)](https://statuscodefyi.com/glossary/dsn/): An SMTP extension (RFC 3461) that provides structured delivery reports — success, failure, or delay — back to the origin... - [Email Header Injection](https://statuscodefyi.com/glossary/email-header-injection/): An attack that exploits improperly sanitized user input to inject additional email headers (BCC, CC, Subject, To) into m... - [SMTP Enhanced Status Codes](https://statuscodefyi.com/glossary/smtp-enhanced-status/): Three-digit dotted codes (e.g., 5.1.1) defined in RFC 3463 that provide more specific diagnostic information than basic ... - [MDN (Message Disposition Notification)](https://statuscodefyi.com/glossary/mdn/): An email mechanism (RFC 8098) where the recipient's mail client sends a notification back to the sender confirming the m... ## Real-Time & Streaming - [WebSocket Frame](https://statuscodefyi.com/glossary/websocket-frame/): The basic unit of communication in the WebSocket protocol. After the initial HTTP upgrade handshake, data is exchanged a... - [gRPC Streaming](https://statuscodefyi.com/glossary/grpc-streaming/): gRPC supports four communication patterns: unary (single request, single response), server streaming (single request, mu... - [SIP Dialog](https://statuscodefyi.com/glossary/sip-dialog/): A peer-to-peer SIP relationship between two user agents that persists for the duration of a call or session. A dialog is... - [WebRTC (Web Real-Time Communication)](https://statuscodefyi.com/glossary/webrtc/): An open framework that enables real-time audio, video, and data communication directly between browsers without plugins.... - [Signaling](https://statuscodefyi.com/glossary/signaling/): The process of coordinating communication between peers before establishing a direct connection. In WebRTC, signaling in... - [ICE Candidate](https://statuscodefyi.com/glossary/ice-candidate/): A network address and port combination that a peer can use for communication in the ICE (Interactive Connectivity Establ... - [Server-Sent Events (SSE)](https://statuscodefyi.com/glossary/server-sent-events/): A unidirectional HTTP-based push technology where the server sends events to the client over a single long-lived connect... - [Long Polling](https://statuscodefyi.com/glossary/long-polling/): A technique where the client makes an HTTP request and the server holds it open until new data is available, simulating ... - [WebSocket Subprotocol](https://statuscodefyi.com/glossary/websocket-subprotocol/): An application-level protocol negotiated during the WebSocket handshake (Sec-WebSocket-Protocol header) that defines the... - [gRPC Metadata](https://statuscodefyi.com/glossary/grpc-metadata/): Key-value pairs sent as headers/trailers in gRPC calls, used for authentication tokens, tracing IDs, and custom applicat... - [SIP Registrar](https://statuscodefyi.com/glossary/sip-registrar/): A SIP server that accepts REGISTER requests and updates the location service database, enabling the SIP network to route... - [WebSocket Ping/Pong](https://statuscodefyi.com/glossary/websocket-ping-pong/): A WebSocket heartbeat mechanism where Ping control frames are sent to check connection liveness, and the recipient must ... - [Event Stream](https://statuscodefyi.com/glossary/event-stream/): The MIME type text/event-stream used by Server-Sent Events, defining a line-based text format with named fields: event (... - [WebSocket Close Code](https://statuscodefyi.com/glossary/websocket-close-code/): A numeric code sent in a WebSocket Close frame indicating the reason for disconnection, defined in RFC 6455. Common code... - [STUN (Session Traversal Utilities for NAT)](https://statuscodefyi.com/glossary/stun/): A protocol (RFC 8489) that helps clients behind NAT discover their public IP address and port by querying a STUN server ... - [TURN (Traversal Using Relays around NAT)](https://statuscodefyi.com/glossary/turn/): A relay protocol (RFC 8656) used when direct peer-to-peer connections fail due to symmetric NAT or restrictive firewalls... - [SDP (Session Description Protocol)](https://statuscodefyi.com/glossary/sdp/): A text format (RFC 8866) for describing multimedia session parameters — codecs, IP addresses, ports, bandwidth, and encr... - [MQTT (Message Queuing Telemetry Transport)](https://statuscodefyi.com/glossary/mqtt/): A lightweight publish/subscribe messaging protocol (ISO/IEC 20922) designed for IoT and constrained networks, running ov... - [STOMP (Simple Text Oriented Messaging Protocol)](https://statuscodefyi.com/glossary/stomp/): A text-based messaging protocol commonly used over WebSocket for connecting browsers to message brokers like RabbitMQ an... - [gRPC-Web](https://statuscodefyi.com/glossary/grpc-web/): A protocol adaptation that enables browser JavaScript clients to communicate with gRPC backends via an HTTP/1.1 or HTTP/... ## Infrastructure - [Service Mesh](https://statuscodefyi.com/glossary/service-mesh/): A dedicated infrastructure layer for managing service-to-service communication in microservices, handling load balancing... - [Sidecar Proxy](https://statuscodefyi.com/glossary/sidecar-proxy/): A proxy deployed alongside each microservice instance to intercept and manage network traffic, implementing service mesh... - [Ingress Controller](https://statuscodefyi.com/glossary/ingress-controller/): A reverse proxy that manages external access to services in a Kubernetes cluster, handling TLS termination, path-based r... - [Service Discovery](https://statuscodefyi.com/glossary/service-discovery/): A mechanism for automatically detecting and locating services in a distributed system, using DNS-based (SRV records) or ... - [Load Balancing Algorithm](https://statuscodefyi.com/glossary/load-balancing-algorithm/): Strategies for distributing traffic across backend servers: round-robin, least-connections, weighted, IP-hash, and consi... - [Blue-Green Deployment](https://statuscodefyi.com/glossary/blue-green-deployment/): A deployment strategy using two identical production environments (blue and green) where traffic is switched from the ol... - [Canary Deployment](https://statuscodefyi.com/glossary/canary-deployment/): A deployment strategy where a new version is gradually rolled out to a small percentage of traffic before full deploymen... - [Health Check Endpoint](https://statuscodefyi.com/glossary/health-check-endpoint/): A dedicated API endpoint (typically /health or /healthz) that returns the operational status of a service, used by load ... - [TLS Termination](https://statuscodefyi.com/glossary/tls-termination/): The practice of decrypting TLS traffic at a load balancer or reverse proxy, forwarding unencrypted HTTP to backend servi... - [Connection Draining](https://statuscodefyi.com/glossary/connection-draining/): A graceful shutdown technique where a server stops accepting new connections but continues processing existing requests ... - [Distributed Tracing](https://statuscodefyi.com/glossary/distributed-tracing/): A method of tracking requests as they propagate through multiple microservices, using trace IDs (W3C Trace Context, Open... - [Observability](https://statuscodefyi.com/glossary/observability/): The ability to understand a system's internal state from its external outputs (logs, metrics, traces), essential for dia... - [Correlation ID](https://statuscodefyi.com/glossary/correlation-id/): A unique identifier (commonly X-Request-ID or X-Correlation-ID) propagated through all services handling a single reques... - [Rate Limiter Algorithm](https://statuscodefyi.com/glossary/rate-limiter-algorithm/): Backend algorithms for enforcing API rate limits, each with different trade-offs in burst tolerance and fairness. Token ... - [Container Orchestration](https://statuscodefyi.com/glossary/container-orchestration/): Automated management of containerized application deployment, scaling, networking, and health — primarily through Kubern... - [Rolling Update](https://statuscodefyi.com/glossary/rolling-update/): A deployment strategy that replaces application instances one at a time (or in small batches), maintaining availability ... - [Readiness Probe](https://statuscodefyi.com/glossary/readiness-probe/): A Kubernetes health check that determines whether a pod is ready to receive traffic, distinct from liveness probes that ... - [SLA / SLO / SLI](https://statuscodefyi.com/glossary/sla-slo-sli/): The three layers of reliability engineering measurement. SLI (Service Level Indicator) is the measured metric, such as r... - [Configuration Management](https://statuscodefyi.com/glossary/configuration-management/): The practice of managing application settings across environments using environment variables, config servers, or featur... - [Zero-Downtime Deployment](https://statuscodefyi.com/glossary/zero-downtime-deployment/): Deployment strategies that ensure the application remains fully available throughout the update process, combining healt... ## Web Standards - [HTTP Semantics (RFC 9110)](https://statuscodefyi.com/glossary/http-semantics/): The core RFC defining HTTP's architecture, including methods, status codes, headers, content negotiation, and conditiona... - [URI (Uniform Resource Identifier)](https://statuscodefyi.com/glossary/uri/): A string that identifies a resource by location (URL) or name (URN), forming the addressing foundation of HTTP and the w... - [MIME Type](https://statuscodefyi.com/glossary/mime-type/): A two-part identifier (type/subtype) that indicates the nature and format of a document, file, or byte stream, standardi... - [CORS Preflight](https://statuscodefyi.com/glossary/cors-preflight/): An automatic OPTIONS request sent by browsers before cross-origin requests with non-simple methods or headers, checking ... - [Content-Disposition](https://statuscodefyi.com/glossary/content-disposition/): An HTTP header indicating whether content should be displayed inline or downloaded as an attachment, and suggesting a fi... - [Transfer-Encoding](https://statuscodefyi.com/glossary/transfer-encoding/): An HTTP header specifying the encoding applied to the message body for transfer (chunked, compress, deflate, gzip), dist... - [Link Header](https://statuscodefyi.com/glossary/link-header/): An HTTP header (RFC 8288) for conveying typed relationships between resources, used for pagination (rel=next), preloadin... - [Origin](https://statuscodefyi.com/glossary/origin/): A combination of scheme, host, and port that defines a security boundary in web browsers, central to the Same-Origin Pol... - [Referrer-Policy](https://statuscodefyi.com/glossary/referrer-policy/): An HTTP header controlling how much referrer information is sent with requests, balancing analytics needs against user p... - [Permissions Policy](https://statuscodefyi.com/glossary/feature-policy/): An HTTP header (formerly Feature-Policy) that controls which browser features (camera, geolocation, autoplay) a page can... - [HSTS Preload](https://statuscodefyi.com/glossary/strict-transport-security/): An extension of HSTS where domains are hardcoded into browsers' built-in HTTPS-only lists, ensuring HTTPS from the very ... - [Structured Headers (RFC 8941)](https://statuscodefyi.com/glossary/structured-headers/): A standardized format for HTTP header values using defined data types (integers, strings, tokens, lists, dictionaries) f... - [Early Hints (103)](https://statuscodefyi.com/glossary/early-hints/): An informational HTTP response that allows servers to send Link headers before the final response, enabling browsers to ... - [Certificate Transparency](https://statuscodefyi.com/glossary/expect-ct/): A web security standard that requires TLS certificates to be logged in public, append-only logs, enabling domain owners ... - [Subresource Integrity (SRI)](https://statuscodefyi.com/glossary/subresource-integrity/): A security feature that ensures resources fetched from CDNs haven't been tampered with, by verifying their cryptographic... - [Web Linking (RFC 8288)](https://statuscodefyi.com/glossary/web-linking/): A framework for expressing typed relationships between resources using Link headers or HTML link elements, enabling mach... - [Proxy Authentication](https://statuscodefyi.com/glossary/proxy-authentication/): An HTTP mechanism where a proxy server requires clients to authenticate before forwarding requests, using the 407 status... - [Conditional Headers](https://statuscodefyi.com/glossary/conditional-header/): HTTP headers (If-Match, If-None-Match, If-Modified-Since, If-Unmodified-Since, If-Range) that make requests conditional ... - [X-Forwarded-For](https://statuscodefyi.com/glossary/x-forwarded-for/): A de facto HTTP header used by proxies and load balancers to identify the originating client IP address when traffic pas... - [Content-Encoding](https://statuscodefyi.com/glossary/content-encoding/): An HTTP response header specifying the compression algorithm applied to the response body before transmission, with comm... ## gRPC & RPC - [gRPC Channel](https://statuscodefyi.com/glossary/grpc-channel/): A logical connection to a gRPC endpoint that handles connection management, load balancing, and name resolution under th... - [gRPC Interceptor](https://statuscodefyi.com/glossary/grpc-interceptor/): Middleware that intercepts gRPC calls for cross-cutting concerns — logging, authentication, metrics, and tracing — simil... - [gRPC Deadline](https://statuscodefyi.com/glossary/grpc-deadline/): A client-specified absolute time by which a gRPC call must complete, propagated across service hops and enforced by DEAD... - [gRPC Status Code](https://statuscodefyi.com/glossary/grpc-status-code/): One of 17 standard numeric codes (0–16) returned by gRPC services, including OK (0), CANCELLED (1), UNKNOWN (2), INVALID... - [gRPC Service Definition](https://statuscodefyi.com/glossary/grpc-service-definition/): A .proto file declaration that defines the RPC methods a service exposes, their request and response message types, and ... - [Unary RPC](https://statuscodefyi.com/glossary/unary-rpc/): The simplest gRPC pattern — a single request from the client receives a single response from the server, analogous to a ... - [Server Streaming RPC](https://statuscodefyi.com/glossary/server-streaming-rpc/): A gRPC pattern where the client sends one request and the server returns a stream of multiple responses, useful for real... - [Client Streaming RPC](https://statuscodefyi.com/glossary/client-streaming-rpc/): A gRPC pattern where the client sends a stream of messages and the server responds with a single message after receiving... - [Bidirectional Streaming RPC](https://statuscodefyi.com/glossary/bidirectional-streaming/): A gRPC pattern where both client and server send streams of messages simultaneously over a single connection. The stream... - [Protobuf Message](https://statuscodefyi.com/glossary/protobuf-message/): A structured data type defined in a .proto file with typed fields, used as the default serialization format for gRPC req... - [gRPC Reflection](https://statuscodefyi.com/glossary/grpc-reflection/): A gRPC service extension that allows clients to discover available services and methods at runtime without prior knowled... - [gRPC Health Checking Protocol](https://statuscodefyi.com/glossary/grpc-health-checking/): A standard gRPC service (grpc.health.v1.Health) that load balancers and orchestrators use to determine if a gRPC server ... - [gRPC Load Balancing](https://statuscodefyi.com/glossary/grpc-load-balancing/): Client-side or proxy-based distribution of gRPC calls — options include pick-first, round-robin, and xDS-based policies ... - [gRPC Retry Policy](https://statuscodefyi.com/glossary/grpc-retry-policy/): A declarative configuration in gRPC service config specifying which status codes are retryable, max attempts, backoff pa... - [gRPC Error Details](https://statuscodefyi.com/glossary/grpc-error-details/): Rich error information attached to gRPC status using google.rpc.Status — includes structured error info, retry info, deb... - [gRPC-Gateway](https://statuscodefyi.com/glossary/grpc-gateway/): A reverse proxy that translates RESTful JSON API requests into gRPC calls, enabling HTTP/JSON clients to consume gRPC se... - [gRPC Keepalive](https://statuscodefyi.com/glossary/grpc-keepalive/): Periodic HTTP/2 PING frames sent by gRPC to detect dead connections and keep NAT mappings alive, configurable via keepal... - [RPC (Remote Procedure Call)](https://statuscodefyi.com/glossary/rpc/): A protocol paradigm where a client invokes a function on a remote server as if it were local, abstracting away network c... - [Protobuf Oneof](https://statuscodefyi.com/glossary/protobuf-oneof/): A protobuf feature where only one field in a group can be set at a time, useful for polymorphic message types and varian... - [gRPC Compression](https://statuscodefyi.com/glossary/grpc-compression/): Message-level compression in gRPC (gzip, snappy, zstd) negotiated via grpc-accept-encoding and grpc-encoding headers, re... ## SIP & VoIP - [SIP INVITE](https://statuscodefyi.com/glossary/sip-invite/): The SIP method used to initiate a session (phone call, video conference), triggering the offer/answer exchange of sessio... - [SIP Proxy Server](https://statuscodefyi.com/glossary/sip-proxy/): An intermediary server that routes SIP requests on behalf of user agents, performing lookup, authentication, and policy ... - [SIP Redirect Server](https://statuscodefyi.com/glossary/sip-redirect/): A SIP server that responds with a 3xx status code containing alternative contact URIs where the target can be reached, w... - [SIP Transaction](https://statuscodefyi.com/glossary/sip-transaction/): A single request-response exchange in SIP identified by the branch parameter in the Via header, with built-in retransmis... - [SIP User Agent](https://statuscodefyi.com/glossary/sip-user-agent/): A SIP endpoint that initiates (UAC — User Agent Client) or receives (UAS — User Agent Server) SIP requests, typically a ... - [SIP Trunk](https://statuscodefyi.com/glossary/sip-trunk/): A virtual connection between a PBX and a service provider that replaces traditional ISDN or analog phone lines, carrying... - [RTP (Real-time Transport Protocol)](https://statuscodefyi.com/glossary/rtp/): A protocol for delivering audio and video over IP networks with timestamps and sequence numbers for synchronization, jit... - [SRTP (Secure Real-time Transport Protocol)](https://statuscodefyi.com/glossary/srtp/): An encrypted extension of RTP that provides confidentiality, authentication, and replay protection for voice and video m... - [SIP ACK](https://statuscodefyi.com/glossary/sip-ack/): The SIP method sent by the caller to confirm receipt of a final response to an INVITE, completing the three-way handshak... - [SIP BYE](https://statuscodefyi.com/glossary/sip-bye/): The SIP method used to terminate an active session (end a call), sent by either party in the dialog and triggering media... - [SIP CANCEL](https://statuscodefyi.com/glossary/sip-cancel/): A SIP method that aborts a pending INVITE transaction before a final response is received, used when the caller hangs up... - [SIP OPTIONS](https://statuscodefyi.com/glossary/sip-options/): A SIP method used to query a server or user agent about its capabilities — supported methods, codecs, extensions, and Ma... - [SIP SUBSCRIBE/NOTIFY](https://statuscodefyi.com/glossary/sip-subscribe-notify/): SIP methods for event notification — SUBSCRIBE requests ongoing updates on a resource (presence status, call state, mess... - [B2BUA (Back-to-Back User Agent)](https://statuscodefyi.com/glossary/b2bua/): A SIP entity that acts as both a UAC and UAS simultaneously, terminating one SIP leg and originating another independent... - [SBC (Session Border Controller)](https://statuscodefyi.com/glossary/session-border-controller/): A network device at the edge of a VoIP network that provides security, NAT traversal, codec transcoding, and SIP normali... - [Codec Negotiation](https://statuscodefyi.com/glossary/codec-negotiation/): The process of agreeing on audio and video codecs (G.711, G.722, Opus, H.264, VP8) between SIP or WebRTC endpoints durin... - [SIP Response Classes](https://statuscodefyi.com/glossary/sip-response-classes/): SIP response codes grouped like HTTP — 1xx (Provisional: processing or ringing), 2xx (Successful: request accepted), 3xx... - [VoIP (Voice over IP)](https://statuscodefyi.com/glossary/voip/): Technology for delivering voice communication and multimedia sessions over IP networks instead of traditional circuit-sw... - [Presence (SIP)](https://statuscodefyi.com/glossary/presence/): A SIP event package that conveys the availability status (online, busy, away, do not disturb) of a user agent, used by i... - [PBX (Private Branch Exchange)](https://statuscodefyi.com/glossary/pbx/): A private telephone switching system that connects internal extensions and routes calls to the public telephone network,... ## FTP & File Transfer - [FTP Active Mode](https://statuscodefyi.com/glossary/ftp-active-mode/): The original FTP data transfer mode where the server initiates a connection back to the client on a client-specified por... - [FTP Passive Mode](https://statuscodefyi.com/glossary/ftp-passive-mode/): An FTP data transfer mode where the client initiates both the control and data connections to the server, solving firewa... - [FTP Control Channel](https://statuscodefyi.com/glossary/ftp-control-channel/): The persistent TCP connection on port 21 used for sending FTP commands and receiving reply codes throughout an FTP sessi... - [FTP Data Channel](https://statuscodefyi.com/glossary/ftp-data-channel/): A separate TCP connection used exclusively for transferring file contents and directory listings in FTP. Unlike the pers... - [SFTP (SSH File Transfer Protocol)](https://statuscodefyi.com/glossary/sftp/): A secure file transfer protocol that runs over SSH on port 22, providing encryption, authentication, and file management... - [FTPS (FTP Secure)](https://statuscodefyi.com/glossary/ftps/): FTP extended with TLS encryption to secure both the control and data channels. Implicit FTPS (port 990) requires TLS fro... - [FTP Reply Code](https://statuscodefyi.com/glossary/ftp-reply-code/): A three-digit status code returned by the FTP server after every client command, structured similarly to HTTP status cod... - [FTP Anonymous Access](https://statuscodefyi.com/glossary/ftp-anonymous/): A mode where users connect to an FTP server with the reserved username 'anonymous' and typically an email address as the... - [FTP Transfer Mode (ASCII vs Binary)](https://statuscodefyi.com/glossary/ftp-ascii-vs-binary/): FTP supports two data transfer modes that determine how file bytes are treated during transmission. ASCII mode converts ... - [FTP Resume (REST Command)](https://statuscodefyi.com/glossary/ftp-resume/): The FTP REST (Restart) command sets a byte offset restart point before a subsequent RETR or STOR command, enabling inter... - [SCP (Secure Copy Protocol)](https://statuscodefyi.com/glossary/scp/): A file transfer protocol that uses SSH for both authentication and encryption, allowing files to be copied between a loc... - [FTP Chroot Jail](https://statuscodefyi.com/glossary/ftp-chroot/): A security technique that restricts FTP users to their home directory by changing the apparent root of the filesystem to... - [WebDAV (Web Distributed Authoring and Versioning)](https://statuscodefyi.com/glossary/webdav/): An extension to HTTP (RFC 4918) that adds methods for collaborative file management on remote web servers, including PRO... - [rsync](https://statuscodefyi.com/glossary/rsync/): A utility for efficient incremental file synchronization that computes the differences between source and destination fi... - [FTP MLSD (Machine-Readable Listing)](https://statuscodefyi.com/glossary/ftp-mlsd/): A modern FTP command defined in RFC 3659 that returns structured directory listings with standardized fact formats (size... - [FTP NAT Traversal](https://statuscodefyi.com/glossary/ftp-nat-traversal/): Techniques for establishing FTP data connections through NAT devices and firewalls, which is complex because FTP embeds ... - [Transfer Integrity](https://statuscodefyi.com/glossary/transfer-integrity/): Mechanisms to verify that files arrive at their destination completely unchanged after a transfer. Common approaches inc... - [FTP over TLS (RFC 4217)](https://statuscodefyi.com/glossary/ftp-over-tls/): The formal specification for securing FTP connections with TLS, covering both the control and data channels. RFC 4217 de... - [File Locking](https://statuscodefyi.com/glossary/file-locking/): A mechanism to prevent concurrent modifications to the same file by multiple clients or processes simultaneously. Adviso... - [Bandwidth Throttling](https://statuscodefyi.com/glossary/bandwidth-throttling/): The intentional limiting of data transfer rates to prevent a single client or process from consuming all available netwo... ## Authentication & OAuth - [OAuth Authorization Code Flow](https://statuscodefyi.com/glossary/oauth-authorization-code/): The most secure OAuth 2.0 grant type for server-side applications, where the authorization server issues a short-lived a... - [OAuth Client Credentials Flow](https://statuscodefyi.com/glossary/oauth-client-credentials/): An OAuth 2.0 grant type for machine-to-machine authentication where the client authenticates directly with the authoriza... - [OAuth Implicit Flow (Legacy)](https://statuscodefyi.com/glossary/oauth-implicit-flow/): A deprecated OAuth 2.0 grant type that returned access tokens directly in the URL fragment after the authorization redir... - [PKCE (Proof Key for Code Exchange)](https://statuscodefyi.com/glossary/pkce/): An OAuth 2.0 security extension (RFC 7636) that prevents authorization code interception attacks in public clients. Befo... - [OIDC (OpenID Connect)](https://statuscodefyi.com/glossary/oidc/): An identity layer built on top of OAuth 2.0 that adds standardized user authentication to the authorization framework. I... - [Refresh Token](https://statuscodefyi.com/glossary/refresh-token/): A long-lived credential issued alongside an access token that allows the client to obtain new access tokens without requ... - [Access Token](https://statuscodefyi.com/glossary/access-token/): A short-lived credential that grants access to protected resources on behalf of a user or client. Access tokens are typi... - [Token Introspection (RFC 7662)](https://statuscodefyi.com/glossary/token-introspection/): An OAuth 2.0 endpoint defined in RFC 7662 where resource servers can send an access or refresh token to the authorizatio... - [Token Revocation (RFC 7009)](https://statuscodefyi.com/glossary/token-revocation/): An OAuth 2.0 endpoint defined in RFC 7009 that allows clients to explicitly notify the authorization server that a token... - [OAuth Scopes](https://statuscodefyi.com/glossary/scopes/): A mechanism in OAuth 2.0 that limits what an access token is permitted to do by attaching a set of named permissions to ... - [JWT Claims](https://statuscodefyi.com/glossary/jwt-claims/): The key-value pairs in the payload section of a JSON Web Token that convey information about the subject and the token i... - [JWK (JSON Web Key)](https://statuscodefyi.com/glossary/jwk/): A JSON data structure defined in RFC 7517 for representing a cryptographic key — RSA, EC, or symmetric — including its k... - [SAML (Security Assertion Markup Language)](https://statuscodefyi.com/glossary/saml/): An XML-based open standard for exchanging authentication and authorization data between an Identity Provider (IdP) and a... - [SSO (Single Sign-On)](https://statuscodefyi.com/glossary/sso/): An authentication scheme that allows a user to log in once and gain access to multiple related but independent applicati... - [MFA (Multi-Factor Authentication)](https://statuscodefyi.com/glossary/mfa/): A security mechanism that requires users to provide two or more independent verification factors from different categori... - [TOTP (Time-Based One-Time Password)](https://statuscodefyi.com/glossary/totp/): An algorithm defined in RFC 6238 that generates short-lived numeric codes from a shared secret key and the current Unix ... - [HTTP Basic Authentication](https://statuscodefyi.com/glossary/basic-auth/): The simplest HTTP authentication scheme, defined in RFC 7617, where the client encodes the username and password as base... - [HTTP Digest Authentication](https://statuscodefyi.com/glossary/digest-auth/): An HTTP authentication scheme defined in RFC 7616 that challenges the client with a server-generated nonce, then expects... - [Session Token](https://statuscodefyi.com/glossary/session-token/): A server-generated opaque identifier, typically stored in a Set-Cookie header, that maps to server-side session data suc... - [Passkey (WebAuthn)](https://statuscodefyi.com/glossary/passkey/): A phishing-resistant passwordless authentication credential based on public-key cryptography, standardized by the FIDO2 ... ## TLS & Encryption - [TLS Versions](https://statuscodefyi.com/glossary/tls-versions/): The evolution of the TLS/SSL protocol — SSL 3.0 (deprecated), TLS 1.0 and 1.1 (deprecated since 2021), TLS 1.2 (current ... - [TLS 1.3](https://statuscodefyi.com/glossary/tls-1-3/): The latest version of the Transport Layer Security protocol (RFC 8446), released in 2018. TLS 1.3 reduces the handshake ... - [Certificate Authority (CA)](https://statuscodefyi.com/glossary/certificate-authority/): A trusted third party that issues digital certificates after verifying that the requester controls the domain (DV), belo... - [Certificate Chain](https://statuscodefyi.com/glossary/certificate-chain/): The ordered sequence of certificates that links a server's leaf certificate back to a trusted root CA. A typical chain i... - [Certificate Pinning](https://statuscodefyi.com/glossary/certificate-pinning/): A security technique where the client hardcodes the expected certificate fingerprint or public key hash and rejects any ... - [Certificate Transparency (CT)](https://statuscodefyi.com/glossary/certificate-transparency/): A public logging framework (RFC 6962) that requires all publicly trusted TLS certificates to be recorded in one or more ... - [Forward Secrecy (PFS)](https://statuscodefyi.com/glossary/forward-secrecy/): A property of a key exchange mechanism where compromising the server's long-term private key does not allow decryption o... - [SNI (Server Name Indication)](https://statuscodefyi.com/glossary/sni/): A TLS extension (RFC 6066) where the client includes the target hostname in the ClientHello message before the TLS hands... - [OCSP (Online Certificate Status Protocol)](https://statuscodefyi.com/glossary/ocsp/): A protocol (RFC 6960) for checking in real time whether a TLS certificate has been revoked by its issuing CA, as a more ... - [OCSP Stapling](https://statuscodefyi.com/glossary/ocsp-stapling/): A TLS extension (RFC 6066) where the server periodically fetches a signed time-stamped OCSP response from the CA and att... - [Let's Encrypt](https://statuscodefyi.com/glossary/lets-encrypt/): A free, automated, and open Certificate Authority operated by the Internet Security Research Group (ISRG) that issues do... - [ACME Protocol (RFC 8555)](https://statuscodefyi.com/glossary/acme-protocol/): Automatic Certificate Management Environment — an IETF standard protocol (RFC 8555) that enables fully automated certifi... - [TLS Session Resumption](https://statuscodefyi.com/glossary/tls-resumption/): Mechanisms that allow a client to skip the full TLS handshake when reconnecting to a server it has previously establishe... - [0-RTT (Zero Round Trip Time)](https://statuscodefyi.com/glossary/zero-rtt/): A TLS 1.3 feature (RFC 8446 Section 2.3) that allows a client to send application data in the very first message of a re... - [Key Exchange](https://statuscodefyi.com/glossary/key-exchange/): The cryptographic process by which two parties agree on a shared secret key over an insecure channel without transmittin... - [PKI (Public Key Infrastructure)](https://statuscodefyi.com/glossary/public-key-infrastructure/): The framework of policies, hardware, software, people, and procedures for creating, managing, distributing, using, stori... - [SSL Stripping](https://statuscodefyi.com/glossary/ssl-stripping/): A man-in-the-middle attack in which an attacker positioned between a client and server intercepts an HTTP request and fo... - [CT Log (Certificate Transparency Log)](https://statuscodefyi.com/glossary/ct-log/): An append-only, cryptographically verifiable log of all TLS certificates submitted to the Certificate Transparency ecosy... - [TLS Fingerprinting (JA3/JA4)](https://statuscodefyi.com/glossary/tls-fingerprinting/): A passive network analysis technique that creates a hash fingerprint of a TLS ClientHello message by extracting fields s... - [Post-Quantum TLS](https://statuscodefyi.com/glossary/post-quantum-tls/): The integration of quantum-resistant key exchange and signature algorithms into TLS to protect against future cryptograp... ## Load Balancing & Proxying - [Layer 4 Load Balancing](https://statuscodefyi.com/glossary/layer-4-load-balancing/): Load balancing performed at the OSI transport layer (Layer 4) using TCP/UDP IP addresses and port numbers to route traff... - [Layer 7 Load Balancing](https://statuscodefyi.com/glossary/layer-7-load-balancing/): Load balancing at the OSI application layer (Layer 7) that inspects HTTP/2/gRPC application data — headers, URLs, cookie... - [Sticky Sessions (Session Affinity)](https://statuscodefyi.com/glossary/sticky-sessions/): A load balancing configuration that ensures all requests from the same client are consistently routed to the same backen... - [Consistent Hashing](https://statuscodefyi.com/glossary/consistent-hashing/): A hashing strategy that maps both keys and servers onto a circular hash ring, so that adding or removing a server causes... - [Weighted Round Robin](https://statuscodefyi.com/glossary/weighted-round-robin/): A load balancing algorithm that extends basic round-robin by assigning a numeric weight to each backend server. Requests... - [Least Connections](https://statuscodefyi.com/glossary/least-connections/): A dynamic load balancing algorithm that routes each new request to the backend server currently handling the fewest acti... - [Forward Proxy](https://statuscodefyi.com/glossary/forward-proxy/): A proxy server that sits between clients and the broader internet, forwarding outbound requests on behalf of those clien... - [Transparent Proxy](https://statuscodefyi.com/glossary/transparent-proxy/): A proxy that intercepts and redirects network traffic without requiring any client configuration — the client is unaware... - [PROXY Protocol](https://statuscodefyi.com/glossary/proxy-protocol/): A protocol created by HAProxy that prepends a small header to a proxied TCP connection containing the original client's ... - [HAProxy](https://statuscodefyi.com/glossary/haproxy/): High Availability Proxy — a free, open-source, high-performance TCP and HTTP load balancer and proxy server widely used ... - [Nginx (as Reverse Proxy)](https://statuscodefyi.com/glossary/nginx-proxy/): Nginx is a high-performance web server that is widely deployed as a reverse proxy and software load balancer in front of... - [Envoy Proxy](https://statuscodefyi.com/glossary/envoy-proxy/): An open-source, high-performance L7 proxy developed by Lyft and donated to the CNCF, designed as the data plane of servi... - [SSL Offloading](https://statuscodefyi.com/glossary/ssl-offloading/): The practice of decrypting incoming TLS traffic at a dedicated load balancer, ADC (Application Delivery Controller), or ... - [GSLB (Global Server Load Balancing)](https://statuscodefyi.com/glossary/global-server-load-balancing/): A technique for distributing traffic across multiple geographically dispersed data centres or cloud regions, directing e... - [Backend Pool](https://statuscodefyi.com/glossary/backend-pool/): The set of origin server instances registered with a load balancer that are eligible to receive forwarded requests. A ba... - [Failover](https://statuscodefyi.com/glossary/failover/): The automatic process of switching incoming traffic from a failed primary server, data centre, or service instance to a ... - [Request Routing](https://statuscodefyi.com/glossary/request-routing/): The set of rules and logic that a load balancer or API gateway uses to determine which backend service or server should ... - [Active-Passive HA](https://statuscodefyi.com/glossary/active-passive-ha/): A high-availability topology in which a primary (active) node handles all production traffic while an identical standby ... - [Connection Multiplexing (Proxy)](https://statuscodefyi.com/glossary/connection-multiplexing/): A proxy optimisation technique where many client-side connections are tunnelled through a smaller number of persistent b... - [xDS (Discovery Service Protocol)](https://statuscodefyi.com/glossary/xds/): A family of gRPC-based data plane APIs used by Envoy Proxy and compatible proxies to receive dynamic configuration from ...