Alienation refers to estrangement in some form or another.

As it relates to communism we should also ask: should we abolish alienation?

Hegel

Alienation comes from Hegel which, for him, was the recognition of the other. Hegel believed that freedom could come from alienation.

Alienation was also seen for Hegel as the separation of man from God, and that the only way humankind can come to know itself is through the separation from God. This idea seems to have been derived from hermetics

Marx

Marxmostly spoke of alienation as it pertained to labor("estranged labor"). This idea later developed into the concept of commodity fetishism

Lacan

Sartre

Heidegger

Misc

Slavoj Zizeksays somewhere that in communismhe wants just "an acceptable amount of alienation."