Glossary

Cache

A store of recently-fetched data, kept close, to avoid fetching it again.

Definition

Caches exist at every layer of the modern web: in your browser, on the operating system, in the CDN, in the application server, and in the database. They're how the internet feels fast despite physically moving bytes around the world.

Cache management is famously hard — incorrect cache rules show users stale content; missing cache rules waste bandwidth and money. The two practical concepts to understand are TTL (how long an entry stays valid) and cache invalidation (telling caches to throw something away).

Example

You visit a news site. Your browser caches the logo, the CSS file, and a hero image. The next page loads without re-downloading them, even from a busy network.

Frequently asked questions

Why does a site sometimes show me an old version?

A cache somewhere is serving a stale copy. A hard reload (Ctrl/Cmd-Shift-R) bypasses your local cache.

Is clearing my cache a privacy fix?

It clears local data but not the server-side records or third-party cookies elsewhere.