Scratch

A horse is a scratch when injury or other necessity causes it to be withdrawn from the race.

Tack

The equipment the horse wears, including saddle and bridle. A jockey typically has their own racing saddle, placed on each horse they ride just before the race.

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.