This question is based on General Literature Principles and Literary Appreciation Comic relief is

Comic relief is a literary and dramatic device in which humorous characters, speeches, or scenes are introduced into a tragic or serious work to provide temporary relief from emotional tension. The key distinguishing feature is that comic relief appears specifically within tragic or otherwise serious works, not in comedies.

It serves a structural purpose: by momentarily lightening the mood, it allows the audience to process heavy emotions before the drama intensifies again. Shakespeare frequently employed this device. The Porter scene in Macbeth, which follows Duncan's murder with drunken comedy, and the Gravediggers in Hamlet, who joke about death just before the climactic final scene, are classic examples.

The description "the use of hearty and wholesome laughter in plays" is too broad and could apply to any comedy, not specifically to the technique of inserting humour into tragedy. "A figure of speech used in comic theatre" is incorrect because comic relief is a dramatic technique, not a figure of speech. And "a device where a play ends in marriage" describes a convention of romantic comedy, not comic relief.