The term alienation has been used by philosophers, psychologists and sociologists to refer to a very wide range of psycho-social disorders including: loss of self, anxiety, anomie, despair, depersonalization, rootlessness, apathy, social disorganization, loneliness, atomization, meaninglessness, isolation, pessimism, and the loss of beliefs or values.
Basically, alienation refers to an individual sense of estrangement from society; or to the state of isolation of those people who, because of their customs, allegiances, behaviour, race or other factors, are marked out by those with whom they mix as "different", strange and sometimes unacceptable. Thus, certain people, races, social classes or groups are alien for various reasons from the point of view of the surrounding society. The ensuing sense of estrangement or self-alienation involves the loss of a sense of identity, a feeling of powerlessness to affect social change and of depersonalization in a large and bureaucratic society.
In Freudian psychology, alienation is the condition of civilized man. Life in a given society implies the acceptance of this society's rules and imposes the necessity to conform to certain roles and expectations. To do so, man represses and transforms vital instincts and impulses which would prove to be asocial. Thus, in becoming acceptable to others, he experiences self-estrangement.
Alienation has become a central notion of contemporary sociology.