A persona is a way of giving a concrete manifestation to a customer segment. Personas were invented by Alan Cooper and introduced in his book The Inmates Are Running the Asylum. Here’s his explanation of how he developed the concept.
Personas are typically developed by interviewing the product’s customers to identify the distinct customer segments. In Windows Vista, we had personas like “Abby” (a nontechnical home user who is the local administrator on the family computer) and her teenage son “Toby”. There was also “Ichiro”, an IT administrator, and probably others I don’t remember. To give the personas some relatability, each one came with a stock photo and a small biography, including details like hobbies.
Within the product teams, it was common to refer to the persona as a real person. Instead of saying, “How would our typical home user feel about this?” we would ask “How would Abby feel about this?” The late Stephen Tolouse described this tendency to me as “slightly creepy”.
It also means that when you join a product, you need to learn who their customer personas are, so you can understand this sort of shorthand when it arises in documents or meetings.
Bonus chatter: As I recall, back in the early 2000’s, the Developer Division had three developer personas: Mort, Elvis, and Einstein. Here’s some discussion of these personas, and how they wound up being controversial.