In Freudian psychoanalysis, ego, from the Latin term for "I", is one of the three primary components of the human mind. It was put forth by Sigmund Freud. Technically, the ego is the entity which is considered to mediate between the id, the super-ego, and the physical world, that is, the element of the mind which forms the interface between the primal desires present in the mind, and the more intellectualized portion, which consists of societal regulations and the suchlike, while taking into account the presence of reality. As such, it is primarily concerned with the preservation of the individual. It may allow some of the desires of the id to be fulfilled, but only if its determination of the potential consequences of this are of such a nature that they will not pose a significant hazard the the individual.
Although much of Freud's theory is considered to be outmoded by modern psychologists and doctors, the entities which he suggested have become somewhat engrained in modern society, and are frequently invoked by laymen to be able to gain a better, though superficial, understanding of the psychoanalytical conceptualization of the human mind.
The term ego has gained a good deal of meaning other than the sense in which which Freud used it, perhaps most notably to refer to self-esteem, although frequently in a negative sense.