The process by which two ad tech companies exchange their respective cookie IDs for the same browser so they can recognize the user in each other's bid requests. Syncing is why a single page load fires dozens of pixels and why programmatic depends on third-party cookies where they still exist.
Cite this entry:
Agency Echelon. "Cookie Sync." Agency Echelon Reference, reviewed September 2026. https://agencyechelon.com/reference/glossary/cookie-sync/