What is a punch line?

A punch line (or punchline) is the final part of a joke, comedy sketch, profound statement, or story, usually the word, sentence or exchange of sentences which is intended to be funny or to provoke laughter or thought from listeners. Few punchlines are inherently funny out of context, but when a comedian sets up the premise and builds up the audience's expectations, the punch line can function as the climactic part of the act.

Punch lines generally derive their humor from being unexpected. The classic stand-up punch line sound is a sting (erroneously called a rimshot) on drums.