Pari-Mutuel

A pool style wagering system, where all money input through betting is divided among those with winning tickets (save for various deductions by the track operators).

Trifecta

A wager picking the first, second and third horses in the exact order. A trifecta box means paying more to ensure the horses can finish in any order in the top three spots.

Scratch

A horse is a scratch when injury or other necessity causes it to be withdrawn from the race.