Third-Party Cookie
01 Definition
Third-Party Cookie meaning: A cookie set by a domain other than the website a user is visiting, used to track across sites.
A third-party cookie is placed by a domain different from the one shown in the address bar, often an ad or analytics provider. It let advertisers recognize users across many sites for retargeting and frequency capping. Major browsers now block or restrict these cookies, pushing the industry toward other methods.
Also called
Why it matters
How Third-Party Cookie fits the work
Third-party cookies powered much of cross-site targeting and measurement for years, so their decline is reshaping how advertisers build audiences and attribute conversions.
In context
When the browser blocked third-party cookies, the retargeting audience shrank sharply because the ad platform could no longer recognize past visitors across other sites.
Practical note
Because Safari and Firefox already block them and support elsewhere is limited, do not build new measurement or audience plans that depend on third-party cookies surviving.