What is the meaning of Dissociation?

The act of dissociating or disuniting; a state of separation; disunion.

The process by which a compound body breaks up into simpler constituents; said particularly of the action of heat on gaseous or volatile substances.

A defence mechanism where certain thoughts or mental processes are compartmentalised in order to avoid emotional stress to the conscious mind.

This term needs a translation to English. Please help out and add a translation, then remove the text {{rfdef}}.

dissociation

Source: wiktionary.org