Bigsmak is correct. Prop (proposition) bets are wagers on anything at all. The superbowl
is notorious for its prop bets. There's always an over/under on how long the national anthem will be, first catch, odd or even points, etc.
There was a great WSOP
episode last year where Helmuth was at a final table & made 3-4 prop bets with Phil Ivey in the audience. Everytime he called an all in, he make a sidebet with Ivey about whether his hand would hold.
He ended up losing more money to Ivey then he made in the tourney.