Authoritative Source
The single system declared as the system of truth for a given identity attribute — the place every other system defers to instead of keeping its own copy.
aka: system of record
Ambiguity about which system is authoritative for which attribute is often the root diagnosis behind a broken identity program. Some attributes need a second authoritative source beyond HR — a project-staffing system, for instance, when who someone is and what they’re currently assigned to genuinely come from different places.