Identity Cluster

An identity cluster is the set of identifiers — cookies, devices and logins — that all belong to one real person, and it is the output of the identity-resolution process.

A person in practice has dozens of identifiers: a mobile cookie, a laptop cookie, an app, various logins. An identity cluster tries to gather all of these under one roof so a 'user' comes closer to a person than to a browser. There are two ways to build it: deterministic, stitching identifiers with a reliable shared key such as a login ID; and probabilistic, guessing from weak signals like IP and behavior, which is inherently error-prone. The real cost of an identity cluster is privacy: the more complete the cluster, the more complete the picture of the person, and that is exactly where data-protection rules tighten. So on today's web, with third-party cookies dead and browsers limiting tracking, building an accurate identity cluster has become both harder and riskier.