What is a “bridge jumper” in horse racing?

Bridge jumper is a term for a horse player who bets big on a heavy favorite, usually to show but sometimes to place. When that happens, so much money is bet on the favorite that it creates a is a horse that it creates oversize payoffs on the other horses if the favorite falters.
Betting all other horses to show is a winning long-term strategy in such a situation, even though you may go quite a while between scores.