It is distinguished from second-party data (another company's first-party data, shared or bought) and third-party data (aggregated by brokers from sources the brand never touched). The operational difference is provenance: you can say exactly who gave it to you, when, and for what.
The post-cookie story is more nuanced than it is usually told. Google reversed its plan to remove third-party cookies from Chrome and moved to a user-choice model instead, so they did not disappear on the timeline the industry prepared for. The direction of travel held anyway: more consent friction, less reliable cross-site tracking, and a higher premium on data a brand owns outright.
Reward programmes are an unusually honest collection mechanism. A cashback or loyalty enrolment produces an identified customer, a verified contact point and a purchase history in exchange for something of stated value — a trade the customer understands, unlike data taken through a consent banner nobody read.
The constraint is that first-party data is only as good as its consent record: under the GDPR the lawful basis and the proof of consent must survive an audit, and an opt-in collected for one channel does not cover another.
Why it matters for brands
First-party data is the only audience asset that does not depreciate when a platform changes its rules. It powers retention, suppression lists, lookalike seeds and measurement — and unlike rented audiences, it stays yours when ad costs rise.