In horse racing, bets on the horses return money in various proportions if the horse places first, second or third. These bets are in the money. All other bets are said to be out of the money and are lost. The horse finishing first is said to Win (no surprise); the second to Place and the third to Show. A bet to Win pays only for a first place finish; a bet to Place pays for first or second, and a bet to Show pays for first, second or third place.
One of the simplest combination bets is an across the board bet, which is actually three bets: a Win, Place, and Show bet, all on the same horse. This alters the possible payouts in an attractive manner, resulting in a three-way win if the horse finishes first.
Picking all three winning horses in their order of finish is called a Trifecta, and pays out significantly more (at much lower odds of success, of course).