Underlay

A horse that is going off at lower odds than it deserves based on performance.

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.

Bullet

A bullet, or bullet workout, is a workout that was clocked as the best time for a certain distance on a given day.