The active user is both a person and an analysis paradigm. An active user is a novice who sits down at a task that he knows next to nothing about and goes to work. Usually the results of such groundless actions are frustrating mistakes, redundant actions, and no apparent progress. Despite these predominantly negative results, the active user accumulates knowledge about the system at an amazing rate. The retention levels of this first-hand experimenting are also very high.
The active user paradigm attempts to codify this behavior, and to make interface design decisions to facilitate this behavior. An example of an interface principle relating to active users is that all actions should be easily reversible. This allows an active user the freedom to make mistakes without adding the frustration of inflicting irrevocable damage to his work in progress.