Walkover
A race in which only one horse competes.  

Washed Out
A horse that becomes so nervous that it sweats profusely. Also known as "washy" or "lathered (up)."  

Weanling
A foal that is less than one-year-old that has been separated from its dam.  

Weigh In
The certification, by the clerk of scales, of a rider's weight before (after) a race. A jockey weighs in fully dressed with all equipment except for his/her helmet, whip and (in many jurisdictions) flak jacket.  

Weight For Age
An allowance condition in which each entrant is assigned a weight according to its age. Females usually receive a sex allowance as well.  

Wheel
Betting all possible combinations in an exotic wager using at least one horse as the key. 

White
A horse color, extremely rare, in which all the hairs are white. The horse's eyes are brown, not pink, as would be the case for an albino.

Wire
The finish line of a race.  

Withers
Area above the shoulder, where the neck meets the back.  

Work
To exercise a horse by galloping a pre-determined distance.