What is the difference between the glossary and the long-form guides?
The glossary tells you what a term means. The guides show how those terms interact in real requests, browser behavior, API design, and debugging work.
Definitions
HTTP Glossary
Use this when you know the term you are seeing in docs, DevTools, or a code review, but want the plain HTTP meaning quickly.
C
CDN (Content Delivery Network)
A CDN is a network of edge servers that cache and serve responses near users. See how cache hits show up in headers and what CDNs do not cache by default.
Content Negotiation
Content negotiation lets one URL serve different formats, languages or encodings based on Accept headers. See q-values, Vary, 406 and the caching traps.
HTTP Cookie
Learn what HTTP cookies are and how browsers store small data pieces for websites. Understand cookie attributes, security, and session management.
CSRF (Cross-Site Request Forgery)
CSRF tricks a logged-in browser into sending an unwanted request to your site. See how it works, why CORS does not stop it and which defenses actually do.
E
H
I
Idempotency Key (Safe POST Retries)
An Idempotency-Key header lets a client safely retry a POST: the server stores the first result and replays it. Learn the protocol, edge cases and conflicts.
Idempotent
Learn what idempotent means in HTTP. Understand why GET, PUT, and DELETE are idempotent, why POST is not, and how idempotency affects API design.
K
M
HTTP Method
Learn what HTTP methods are and how they define actions on resources. Understand GET, POST, PUT, DELETE, PATCH, and other methods with examples.
MIME Type (Media Type)
A MIME type, or media type, is the type/subtype label in Content-Type that tells clients how to interpret a body. Covers nosniff and blocked-script errors.
O
P
HTTP Payload
Learn what HTTP payload means and how message bodies carry data in requests and responses. Understand JSON, form data, and binary payloads.
Preflight Request (CORS OPTIONS)
A CORS preflight is an automatic OPTIONS request the browser sends before a cross-origin request to check permission. See when it fires and how to answer it.
R
HTTP Request
Learn what an HTTP request is and how clients send messages to servers. Understand request structure, methods, headers, and body components.
HTTP Response
Learn what an HTTP response is and how servers reply to client requests. Understand response structure, status codes, headers, and body content.
Reverse Proxy
A reverse proxy sits in front of origin servers and forwards client requests to them. Learn the headers it adds, nginx proxy_pass pitfalls and 502/504 causes.
S
Same-Site vs Same-Origin
Site and origin are not the same. Learn how eTLD+1 and the Public Suffix List define same-site, and why it decides SameSite cookie and CORS behavior.
HTTP Session
Learn what HTTP sessions are and how they maintain state across stateless HTTP requests. Understand session cookies, tokens, and server-side storage.
SNI (Server Name Indication)
SNI is a TLS extension that sends the hostname in the ClientHello so one IP can serve many certificates. Learn debugging with curl and nginx upstream pitfalls.
HTTP Status Code
Learn what HTTP status codes are and how they indicate request results. Understand 1xx, 2xx, 3xx, 4xx, and 5xx code classes with common examples.
T
TLS Handshake
The TLS handshake negotiates keys and authenticates the server before HTTP data flows. See the TLS 1.3 round trip, ALPN, session resumption and 0-RTT risks.
TTFB (Time to First Byte)
TTFB is the time from starting a request until the first byte of the response arrives. Learn what it includes, how to measure it and what usually inflates it.
U
X
What This Glossary Is For
Use the glossary when you know the term but want the protocol meaning, not a framework-specific shortcut. It is the fastest way to get oriented before diving into a guide, a bug, or a tooling readout.
- Read a glossary page first when two teams are using the same word differently.
- Jump to a guide when the term is clear but the implementation tradeoffs are not.
- Use these definitions as the shared vocabulary for methods, headers, status codes, and cookies.
Good Places To Start
If you are new to HTTP terminology, these pages cover the terms that unlock the rest of the site fastest.
- HTTP Request
- Learn what an HTTP request is and how clients send messages to servers. Understand request structure, methods, headers, and body components.
- HTTP Response
- Learn what an HTTP response is and how servers reply to client requests. Understand response structure, status codes, headers, and body content.
- HTTP Header
- Learn what HTTP headers are and how they provide metadata about requests and responses. Understand common headers like Content-Type and Authorization.
- HTTP Method
- Learn what HTTP methods are and how they define actions on resources. Understand GET, POST, PUT, DELETE, PATCH, and other methods with examples.
- HTTP Status Code
- Learn what HTTP status codes are and how they indicate request results. Understand 1xx, 2xx, 3xx, 4xx, and 5xx code classes with common examples.
- HTTP Cookie
- Learn what HTTP cookies are and how browsers store small data pieces for websites. Understand cookie attributes, security, and session management.
Good Questions To Start With
When should I use the glossary instead of search?
Use the glossary when you already know the word but want the exact meaning. Use search when you know the symptom or task, but not the HTTP term behind it.
Why do terms like request, response, and header get separate pages?
Because they are related but not interchangeable. Keeping them separate makes the definitions tighter and helps you move from a vague mental model to the exact protocol concept you need.