A consolation prize given to a loser in a contest. Some tournaments offer these kinds of prizes to the worst player. I've seen it in billiards and in golf tournaments.

Monty Hall of Let's Make a Deal used to award booby prizes on his show. The prize was called a Zonk and it could be any number of ridiculous objects: a giant rocking horse, a camel, a goat, or a can filled with garbage.

The phrase originates from the word booby: a dunce, idiot, or loser.