What it is
A cookie is a small value a site asks the browser to store. A
third-party cookie belongs to a site different from the page you are viewing, often through embedded content such as an ad or widget. It can help recognize a browser across several pages where that third party appears. A first-party cookie from the site you opened may instead keep you signed in or remember a shopping cart.
A practical example
You read two unrelated sites that both embed content from the same advertising network. If the browser permits the network's cookie in both contexts, that network may link the visits. Blocking third-party cookies can reduce this form of tracking, but a sign-in widget or embedded service might then need a narrow exception. MDN's
web privacy guide explains the distinction and why browser policies differ.
What it does not mean
A cookie is not automatically an executable virus. Removing all cookies can sign you out without fixing a compromised account. If someone stole an active sign-in cookie, changing a browser preference alone does not end that session; revoke active sessions at the service. See our
session-cookie explanation.
