A persona is a fictional, named profile that represents a real audience segment, used to keep teams designing for a specific person rather than an abstraction.
Personas are a communication device, not research. They are useful when they are grounded in real data and dangerous when they are invented in a workshop and then treated as fact.
The parts that change decisions are goals, frustrations, and the moment of need. The parts that rarely change decisions are stock photos and favourite coffee orders.