← DictionaryThird-Party Cookie
A cookie set by a domain other than the one being visited, used for cross-site tracking.
Tracking across other people's sites. Being phased out.
What It Is
You will find Third-Party Cookie in the Technology layer, alongside the rest of Tracking. In practice it means this: a cookie set by a domain other than the one being visited, used for cross-site tracking.
It is a mechanism rather than an opinion: set up properly it behaves predictably, and set up badly it fails just as predictably. Once it is defined that clearly, arguments about it usually stop.
How It's Used
You will usually meet Third-Party Cookie in build decisions, tooling and the plumbing behind a working system. It is usually discussed together with Cookie, Retargeting and Attribution. The practical test is whether it is configured, documented and actually working.
Why It Matters
Third-Party Cookie is cheap to get right early and awkward to fix late. When it is unclear, small technical debts compound into a rebuild. It is worth pinning down before anyone builds on top of it.
Think of plumbing. Nobody admires it, everybody notices when it leaks. Tracking across other people's sites. Being phased out.
Termshift™
How the meaning shifts depending on who is using it, and where.
Practitioners use Third-Party Cookie as shorthand and expect no explanation — a cookie set by a domain other than the one being visited, used for cross-site tracking.
Outside the industry, most people would just say: tracking across other people's sites. Being phased out.
The Bottom Line
If you only keep one thing about Third-Party Cookie: tracking across other people's sites. Being phased out. Everything after that is detail.