What does "header" mean in programming?
header is one of the most common terms in software development. This guide explains what it means, how it is used in practice, and why it matters, with real examples from the developer world.
Definition
Key-value metadata attached to an HTTP request or response, separate from the body. Request headers carry authentication tokens (Authorization), content type (Content-Type), and client information. Response headers carry caching instructions (Cache-Control), CORS permissions, and rate limit information.
Example
"The API requires an Authorization: Bearer <token> header on every request. Without it, the server returns a 401."
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