Daily Double
Type of wager calling for the selection of winners of two consecutive races, usually the first and second or the last two.  

Daily Racing Form
A daily newspaper containing news, past performance data and handicapping information.

Dam
The female parent of a foal.  

Dark Bay or Brown
A horse color that ranges from brown with areas of tan on the shoulders, head and flanks, to a dark brown, with tan areas seen only in the flanks and/or muzzle. The mane, tail and lower portions of the legs are always black unless white markings are present.  

Dead Heat
Two or more horses finishing a race in a tie.  

Deep Stretch
A position very close to the finish line in race.  

Derby
A stakes event for three-year-olds.  

Disqualification
Change in order of finish by officials for an infraction of the rules.  

Distaff
Referring to races for female horses.

Distanced
Horse so far behind the rest of the field of runners that it is out of contact and unable to regain a position of contention.  

Dogs
Rubber traffic cones (or a wooden barrier) placed at certain distances out from the inner rail, when the track is wet, muddy, soft, yielding or heavy, to prevent horses during the workout period from churning the footing along the rail.

Dosage
A system that identifies patterns of ability in horses based on a list of prepotent sires, each of whom is a "superior sire." The Dosage system puts these sires into one of five categories brilliant, intermediate, classic, solid and professional, which quantify speed and stamina.

Dosage Index
A mathematical reduction of the Dosage profile to a number reflecting a horse's potential for speed or stamina. The higher the number, the more likely the horse is suited to be a sprinter. The average Dosage index of all horses is about 4.0.  

Driving
A horse that is all out to win and under strong urging from its jockey.  

Drop Down
A horse meeting a lower class of rival than it had been running against.  

Dwelt
Extremely late in breaking from the gate.