Id...

Sigmund Freud popularized the term and defined libido as the instinct energy or force, contained in what Freud called the id, the largely unconscious structure of the psyche. Freud pointed out that these libidinal drives can conflict with the conventions of civilized behavior, represented in the psyche by the superego. It is this need to conform to society and control the libido that leads to tension and disturbance in the individual, prompting the use of ego defenses to dissipate the psychic energy of these unmet and mostly unconscious needs into other forms. Excessive use of ego defenses results in neurosis. A primary goal of psychoanalysis is to bring the drives of the id into consciousness, allowing them to be met directly and thus reducing the patient's reliance on ego defenses.[1]

According to Swiss psychiatrist Carl Gustav Jung, the libido is identified as psychic energy. Duality (opposition) that creates the energy (or libido) of the psyche, which Jung asserts expresses itself only through symbols: "It is the energy that manifests itself in the life process and is perceived subjectively as striving and desire." (Ellenberger, 697)

Defined more narrowly, libido also refers to an individual's urge to engage in sexual activity. In this sense, the antonym of libido is destrudo.