First-party data
First-party data is information a business collects directly from its own customers and audiences: purchases, sign-ups, site behaviour, CRM records. In media it powers retargeting, exclusions, lookalike seeds and measurement, and its importance has grown as third-party signals decline.
In practice
The practical uses in planning: suppress existing customers from prospecting, seed lookalikes with the best ones, retarget engaged non-converters, and pass conversion values back for optimisation.
Consent and governance are part of the asset - data you cannot lawfully activate is not an asset at all.