Dam:  A mare, the mother of a foal.  A female parent's mother is called a granddam, or a second dam.

Dandy brush:  A cleaning brush.

Dished face:  Head with a concave facial profile.

Distaff side:  The female line or bottom line in a pedigree, back to the tap root.

Dolichomorphic:  A group of classification in which may be found breeds that are characterized by long-leggedness and a capacity of higher speeds, such as the Turkoman.

Dressage:  The training of a horse.  Basis of all horsemanship.  It includes breaking and basic schooling, as well as the more advanced, precision movements that are performed by well-schooled, obedient horses.  Purpose is training and complete mastery of the horse.