Definition of: id

(id) noun
1. Biol. In Weismann's theory of heredity, a unit of germ plasm representing the characteristics of an ancestral member of the species: supposedly composed of determinants, which are made up of biophores.
2. Psychoanal. The concealed, inaccessible part of the psyche, seated in the unconscious, independent of a sense of reality, logic, and morality, but actuated by fundamental impulses towards fulfilling instinctual needs; the reservoir of psychic energy or libido. [Def. 1, short for IDIOPLASM; def. 2, <NL <L id it, trans. of G es]