A persona is a representation of a virtual user, based on empirical data. The description includes a concise summary of characteristics of the user, their experience, goals and tasks, pain points, and environmental conditions. Personas describe the target users, giving a clear picture of how they're likely to use the system, and what they’ll expect from it.
The advantage of persona is a common understanding over the development team and the dissociation from the personal point of view. In contrast to alternative methods like lead user(s) (usually the developer itself), a panel of real users or a description per sociological milieus, persona are more representative, faster to access, and easier to understand. Its a very efficient method.