Third-party cookie

Meaning

A third-party cookie is a cookie that belongs to a different site from the one in the address bar, usually because content from that other site is embedded. Legitimate uses include a payment frame that recognises a returning customer, a chat widget that keeps a conversation and a shared sign-in. The same technique has been used for cross-site tracking, which is why many browsers now block or partition these cookies. Behaviour differs by browser, version and settings, so test embeds in several browsers. See also: First-party cookie, Partitioned cookie, SameSite None, the guide "First-Party, Third-Party and Partitioned Cookies".