Apprentice

A new jockey who has not ridden a certain number of winners in a specified time period.

Also Eligible

A horse that is entered but does not draw into the body of the field due to too many entries, and thus is not permitted to start unless there are enough scratches to shrink the field size.

Workout

A workout is a timed sprint over varying distances prior to a race, meant to get a horse fit enough for competition.