Catharsis is a form of emotional cleansing first defined by the Greek philosopher Aristotle. It originally referred to the sensation that would ideally overcome an audience upon finishing a tragedy. The fact that there existed those who could suffer a worse fate than them was to them a relief, and at the end of the play, they felt ekstasis (literally, astonishment), of which the modern word ecstasy is derived from. While seemingly related to schadenfreude, it is not, however, in the sense that the audience is not intentionally led to feel happy in light of others' misfortunes; in an invariant sense, their spirits are refreshed through having greater appreciation for life.
The term Catharsis has been adopted by modern psychotherapy to describe the act of giving expression to deep emotions often associated with events in the individuals past which have never before been adequately expressed.