Variously defined, but principally the positive theory of the German philosopher Georg Wilhelm Friedrich Hegel (1770-1831) and the critical theory of the German political economist Karl Marx (1818-1883) of consciousness in history.
Hegel: human history consists of the progressive divisions or alienations of consciousness, whereby complexity and identity are recognized in growing division. Spirit creates its word in the act of knowing it. We know things only when they become separate from us.
Marx: capitalism is characterized by the separation or alienation of the workers from what they make, from the productive process, from their true nature or 'species being' and from other people.
R Schacht, Alienation (New York, 1970)