Cache-Control
The HTTP header that tells browsers and CDNs how (and how long) they may cache a response.
Cache-Control is the HTTP header that governs caching: directives like max-age=3600 (cache for an hour), no-store (never cache), no-cache (revalidate before use), and public/private (may a shared cache like a CDN store it). It is how you control the browser and CDN caching layers.
Worked example: a hashed static asset (app.abc123.js) gets Cache-Control: public, max-age=31536000, immutable — cache it for a year, because a content change produces a new filename; an HTML page gets no-cache so it always revalidates. Gotcha: aggressive caching without content-hashed filenames is how users get stuck on a stale version after a deploy — the fix is “cache assets forever, name them by content hash, never cache the HTML that references them”; and ETags let a revalidation return 304 (unchanged) cheaply.