Underlay

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

Main Track Only

A horse entered for main track only (MTO) is one hoping the weather forecast or track conditions will move the race off the turf course and onto the main track. They are scratched the morning of the race if the conditions stay dry.

Minus Pool

A pari-mutuel pool – typically a show pool - where one horse is so heavily bet that after deductions there is not enough money left to cover the prescribed minimum on each bet.