The Latin word for ‘desire’ or ‘wish’ appropriated by psychoanalysis to name the psychical energy of the id. Freud, Sigmund was the first to use this term in this way, but it is now widely used, even outside of psychoanalytic literature where it has become a ‘polite’ code phrase for an individual’s sexual appetite. Freud initially thought the libido was exclusively sexual in nature, and confined to the instinct, so he opposed it to the ego, which is the product of a compromise with the instincts; but he later came to think that the ego also has libidinal energy and revised his theory accordingly. In his more mature works, libido is the psychical dimension of sexual excitation---its effects may be felt somatically, but it is not a somatic concept. Libido is perhaps better understood as belonging more to the order of the drive than the instincts, which chimes well with Freud’s later positioning of it as the opposite of the death-drive. Some scholars, Jung, Carl and Deleuze, Gilles in particular, reject Freud’s idea that libido is necessarily a sexual energy and treat it as a kind of life-force, an energy pervading all human activity.