Story structure
Catharsis
From the Greek for purification or cleansing: the release of pity and fear that Aristotle assigned to tragedy.
Catharsis comes from the Ancient Greek katharsis, "purification" or "cleansing," and in its modern sense names the purging of thoughts and emotions by expressing them, "with a desired result of renewal and restoration." Its literary sense comes from Aristotle: in the Poetics, tragedy shows heroic action that, "through pity and fear it effects relief to these and similar emotions." What the relief actually is has been argued for centuries, and the article files the debate as open: purgation, Lessing's purification that brings pity and fear into balance, or an intellectual clarification.
For the working writer, catharsis names what tragic structure is for: the hamartia that sets the fall in motion ends in a release the audience feels as earned. It lands after the peak, which is why the denouement exists: the release needs somewhere to happen. A tragedy that skips it reads as merely bleak; one that skips the suffering reads as unearned.