Third-party cookie is a cookie stored by a domain that is not the site in the address bar: an ad network, a social pixel, an embedded player. First-party cookies come from the site itself (cart, login, language). Third-party ones follow you from shop to news site to social feed.
That follow-you behavior powers retargeting and much cross-site analytics. It also triggers GDPR / CCPA consent banners and a clear privacy policy. Safari, Firefox, and Brave already restrict these cookies; Chrome did not kill them in 2025 after years of “cookieless future” talk. Your strategy should not wait on one browser’s roadmap. First-party data — email list, accounts, loyalty — stays yours.
A real-life example of a third-party cookie
You browse boots on a small Atlanta store, leave, then see those boots on a recipe blog the next morning. The store didn’t put a stamp on the blog; an ad partner did, using a third-party cookie. The store’s own “remember my cart” cookie is first-party — useful, and a different privacy story.
Don’t rewrite your whole stack because of a rumored Chrome deadline. Do test tracking in Safari as well as Chrome, and keep consent copy honest. Store-level context: E-commerce Technical Pillars.