Jim Carrey makes funny faces

Humour or humor (see spelling differences) is the tendency of particular cognitive experiences to provoke laughter and provide amusement. The term derives from the humoral medicine of the ancient Greeks, which taught that the balance of fluids in the human body, known as humours (Latin: humor, "body fluid"), controlled human health and emotion.
People of all ages and cultures respond to humour. Most people are able to experience humour—i.e., to be amused, to smile or laugh at something funny—and thus are considered to have a sense of humour.