The process of storing frequently accessed data in temporary storage for faster retrieval on subsequent requests. Browser caching stores assets locally while server caching reduces database queries and processing time. Understanding caching helps troubleshoot why changes don't appear immediately—you may need to clear cache or wait for CDN propagation.

Metadata sent with HTTP requests and responses that controls behavior such as caching, security policies, and content handling. Common examples include Cache-Control, Content-Security-Policy, and Strict-Transport-Security.