The sum total of all the characteristics of a person---including the mental, moral, physical, and social qualities---as they are perceived by other people. The word may be used either in a popular sense, in which the meaning is linked simply to the type of person as seen by others, or in a psychological sense, in which the meaning is more complex and sometimes less obvious.

Psychoanalysts regard personality as the result of the interaction between instinct and the environment. Other schools of psychology and psychiatry have more complicated explanations, combining the effects of heredity, upbringing, experience, and biochemical factors.

One of the most widely followed divisions is Carl Jung's categories of extroverted and introverted personalities. The distinction in technical terms is that the extrovert directs his libido and instinctual energy toward the environment, whereas the introvert has weak instinctual energy and directs it inward toward himself. Most persons combine aspects of both personality types, and the extreme examples of either can be recognized by their behavior.

Personality may have no medical connotations at all. To describe a person as having an "unpleasant" personality or a "miserable" personality is not to suggest that he is in any way mentally ill. On the other hand, there are various defects in behavior or life-style that are regarded widely as personality disorders. These are characterized by pathological trends in personality structure, with or without anxiety---in most cases manifested by a lifelong pattern of abnormal action of behavior.

Sociopathic personality disturbance for instance, may be a pathological relationship between the person and the society in which he lives, manifested by irresponsibility, inability to feel guilt, impulsiveness, and poor interpersonal relationships.

Various mental disorders often are expressed in terms of personality. Sufferers will be categorized as paranoid personalities, borderline personalities, schizoid personalities, or dependant personalities. There are also authenticated cases of multiple personality, which most authorities believe are delusional in character. In all these cases personality is distorted into an abnormal type by the underlying mental or emotional disorder.