First-party data
In practice, for a UK buyer
The paragraph above is the neutral answer. This is the part a vendor glossary leaves out.
The most valuable targeting asset most advertisers own and the hardest to activate on premium channels, because getting a list from your database onto a television requires an identity bridge that does not compromise the list. Consent-chained identifiers such as EUID exist for exactly this. Being accurate about the current state: AdBuyMCP's compiled CTV plans carry an empty EUID audience list, so that bridge is designed rather than in use, and the adapter behind it is a fail-closed stub pending an operator agreement.
What this one connects to
Most confusion in media buying comes from two adjacent terms being used interchangeably, so these are the neighbours worth reading next.
Third-party data
Audience data collected by one organisation and licensed to another for targeting, with no direct relationship between the licensee and the people described. Sold as segments through data marketplaces attached to buying platforms.
European Unified ID (EUID)
A consent-based identifier for European advertising, derived from a hashed email or phone number provided with consent, designed to let first-party audiences be addressed across publishers without third-party cookies.
Identity resolution
The process of deciding that two different identifiers refer to the same person or household, so that behaviour seen under one can be joined to the other.
Lookalike audience
An audience built by finding people who resemble a seed group — usually the advertiser's existing customers — on whatever signals the platform holds. The resemblance model is the platform's and is not disclosed.
More on targeting and identity
How an audience is described to a seller, and how much of the description survives. Most of the honest difficulty in media buying lives here.
45 minutes. Bring a real brief and we compile it live. You describe one audience and watch it compile into seven targeting specifications, each with the score for how much of the definition survived.
Talk it through