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.

State-Bred

A horse bred in a particular state and thus eligible to race in restricted state-bred races. These can be anything from maiden races to stakes events.

Underlay

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