Third-party cookie definition (noun)
A third-party cookie is a cookie that’s used on a site other than the one that created it. For example, Site A is using a third-party cookie created by Site B. A user visits Site A, the third-party cookie is attached to the user’s browser, and now Site B can collect data about that user without the user ever visiting Site B.
Third-party cookies are typically used to track users’ browsing history and web-surfing behavior for online advertising purposes.