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.

Underlay

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

Fractions

The times recorded during the race; with timing starting just past the gate or when the gates open, then parroted for the quarter, half, three-quarters etc. Used as an indication of ability and speed.