From DMJ Productions

Personality is any person's or individual's collection of interrelated behavioral, cognitive and emotional patterns that biological and environmental factors influence; these interrelated patterns are relatively stable over long time periods, but they change over the entire lifetime. While there is no generally agreed-upon definition of personality, most theories focus on motivation and psychological interactions with the environment one is surrounded by. Trait-based personality theories, such as those defined by Raymond Cattell, define personality as traits that predict an individual's behavior. On the other hand, more behaviorally-based approaches define personality through learning and habits. Nevertheless, most theories view personality as relatively stable.

The study of the psychology of personality, called personality psychology, attempts to explain the tendencies that underlie differences in behavior.

From Wikipedia