As Chaucer's monk says, before he begins to "biwayle in maner of tragedie": Tragedie is to seyn a certeyn storie Of him that stood in great prosperitee, And is y-fallen out of heigh degree Into miserie, and endeth wrecchedly. A comedy, on the other hand, is a drama in which the characters are placed in more or less humorous situations.
In the Middle Ages, this was thought to be the very essence and meaning of tragedy, as we may see from Chaucer's lines: "Tragedie is to seyn a certeyn storie, As oldë bokës maken us memorie, Of him that stood in gret prosperitee, And is y-fallen out of heigh degree Into miserie, and endeth wrecchedly."