Rabbit

Also known as a pacemaker; this is a horse with no expected chance of winning but is used to prompt a quick pace on the front end of the race to the benefit of a stablemate who is a closer.

Across the Board

Refers to betting on a horse to finish first, second, and third to cover any of those scenarios happening during a race

Sloppy

A wet racetrack condition, typically with a firm base and water settling on top.