What is Third-Party Cookie?
A tracking cookie set by a domain other than the one the user is currently visiting, traditionally heavily used for cross-site ad retargeting.
If you are reading an article on a news site, and that site has a Facebook Pixel installed, Facebook can load a cookie in your browser. Because the domain in your URL bar (the news site) doesn't match the domain setting the cookie (facebook.com), it is a third-party cookie.
The Death of Third-Party Cookies
Safari (Apple) and Firefox have blocked third-party cookies by default for years. Google Chrome is also actively phasing them out. This makes traditional ad retargeting significantly harder, which is why Server-Side Tagging and First-Party data collection strategies have become critical for modern marketers.
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