Third-Party Data.

Third-party data is audience information collected by a company that has no direct relationship with the end user — typically data brokers, ad networks, or data aggregators who compile behavioural profiles from across many websites and apps. Marketers historically used third-party data to target ads at audience segments based on demographics, interests, and purchase intent signals inferred from cross-site tracking.

The Decline of Third-Party Data

Third-party cookies — the primary mechanism for cross-site tracking — are being phased out. Firefox and Safari already block them by default; Chrome followed with cookie deprecation proposals. Apple's ATT framework requires explicit opt-in for cross-app tracking on iOS. These changes are eroding the availability and accuracy of third-party data, pushing marketers toward first-party and zero-party data strategies.

Third-Party Data vs Other Data Types

Zero-party data is intentionally shared by the user (preferences, surveys). First-party data is collected directly by the brand. Second-party data is another company's first-party data purchased directly (e.g., buying a media publisher's subscriber data). Third-party data is aggregated from multiple unknown sources. As privacy regulations tighten, the hierarchy has inverted: zero and first-party data are now the most valuable, while third-party data's value and availability have declined sharply.