Oaks
A stakes event for three-year-old fillies.  

Objection
Claim of foul lodged by rider, patrol judge or other official after the running of a race. If lodged by official, it is called an inquiry.  

Odds-on
Odds of less than even money.  

Official
1) Notice displayed when a race result is confirmed. 2) Used to denote a racing official.  

Off-track Betting
Wagering at legalized betting outlets usually run by the tracks, management companies specializing in parimutuel wagering, or, in New York State, by independent corporations chartered by the state. Wagers at OTB sites are usually commingled with on-track betting pools.  

On the Bit
When a horse is eager to run. Also known as "in the bridle."  

On the Board
Finishing among the first three.  

On the Muscle
Denotes a fit horse.  

On the Nose
Betting a horse to win only.  

OTB
Abbreviation for off-track betting. 

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.