The Programmatic Glossary
A practical glossary designed to help marketers, advertisers and ad-tech professionals understand the terminology that powers programmatic advertising
Identity & Data
Third-Party Cookie
A small file placed on a user's device by a company other than the website they are visiting, typically an ad tech platform, tracker or analytics provider. Third-party cookies were the foundation of cross-site user tracking and personalised advertising for decades, but are now being phased out.
HOW IT WORKS
When a user visits a website that includes a third-party tracker (such as an SSP, Supply-Side Platform, or DMP, Data Management Platform, pixel), that tracker places a cookie on the user's device. When the user visits another site with the same tracker, their cookie is recognised and their browsing history is linked. This enables audience building and retargeting across the web.
EXAMPLE
A user researches holidays on a travel aggregator. The site's retargeting partner places a cookie. The user then visits a news site, which also runs the same retargeting technology. The partner recognises the cookie and serves a hotel ad. Without third-party cookies, this cross-site recognition no longer works.
RELATED TERMS
First-Party Data | Identity Solution | Universal ID | Contextual Targeting | Retargeting
