Personas are commonly used tools in UX design. It's a representation of the real target audience data, collected in previous research phases such as user interview.

Proto personas, meant to quickly align the team’s existing assumptions about who their users are, but not based on (new) research

Qualitative personas, based on small-sample qualitative research, such as interviews,  usability tests, or field studies

Statistical personas, where initial qualitative research informs a survey instrument that is used to gather a large sample size, and the personas emerge from statistical analysis