Underlay

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

Bobble/Stumble

A slip or a duck from a horse trying to leave the starting gates, often caused by the surface giving way under the feet. This can range from a mild misstep to a stumble down to their knees.

Apprentice

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