Third-party cookie

A third-party cookie is set by a domain other than the site being visited, and was historically how advertisers recognised the same browser across different sites for targeting and measurement. Browser restrictions, led by Safari and Firefox, made that recognition unreliable and pushed teams back onto their own logged-in and consented data. First-party cookies set on your own domain still work, although a cookie written by client-side script can have its lifetime shortened by the browser.