Out of the Money
A horse that finishes worse than third.  

Overlay
A horse going off at higher odds than it appears to warrant based on its past performances.  

Overnight
A sheet published by the racing secretary's office listing the entries for an upcoming racing card.  

Overnight Race
A race in which entries close a specific number of hours before running (such as 48 hours), as opposed to a stakes race for which nominations close weeks and sometimes months in advance.  

Overweight
Surplus weight carried by a horse when the rider cannot make the required weight.