What it means
Email addresses, phone numbers, purchase history, on-site behaviour, CRM records — data you own, gathered with permission. It is distinct from third-party data bought from outside aggregators, which is fast disappearing.
Why it matters
Privacy rules (UAE PDPL, GDPR) and browser changes are killing third-party tracking. First-party data is what you activate instead: custom audiences, lookalikes, server-side conversions, and lifecycle marketing. The brands that win the next few years are the ones building consented first-party data assets now.