Personas are abstract representations of groups of audience members, with particular sets of capabilities, dispositions, and motivations grouped together as a persona. The purpose of categorizing the audience into multiple personas is to make it easier to think about and design for the different types of audience members an experience is likely to have without just assuming that the audience is homogeneous.
There are many categorization systems that are effectively personas: demographics, psychographics, Bartle type, Meyers-Briggs type, and many more. These alone could be used as personas when creating an experience, although usually it works better to create specific personas for the particular experience being created. These custom personas will often use labels from standard categorization systems as a short-hand for a particular set of capabilities, dispositions, or motivations. Personas that have affinities for (or aversions to) particular types of elements (a preference for narrative elements, for example), types of engagement (an aversion to challenge, for example), or levels of tension (a desire for extremely high tension, for example) can be particularly useful, as they often give a lot of clarity to design decisions that must be made.
Target AudienceThe personas used for a particular experience should be selected to cover as much of the target audience for the experience as possible. Using personas that are outside the target audience is generally not useful (except perhaps to be clear that a particular persona is deliberately not being targeted by a particular experience). If the target audience of an experience is represented as a circle (see diagram to the right), the personas selected should cover as much of that circle as possible.
Personas can be very broad (casual players) or very narrow (combat veterans interested in stories about the emotional effects of war). Broad personas are good because they cover a larger portion of the audience, but narrow personas are often more evocative and easier to empathize with. If the target audience is small, the personas used will often be narrow. Narrow personas can be used with large target audiences, but there is more of a danger that important personas will be missed.
There is a limit to the number of personas that it is useful to consider for a particular experience. Three to five personas tend to work well, and even just two can be useful (animated movie viewers could be split into kids and adults, for example). Often it is useful to have one persona represent the middle of the target audience (the really hard-core fans), with other personas surrounding it to cover the rest of the audience.
Once there are more than five personas being considered, though, it becomes harder to keep them all in mind while making decisions. Six to twelve personas could work in specific cases, but only if there is a real need to break down the audience into many different categories. Using more than twelve personas would generally only be done when doing long-term research into different types of audience members.