stan·dard·bred or Stan·dard·bred 
(stăndərd-brĕd′)
(stăndərd-brĕd′)n.
Any of an American breed of trotting and pacing horses developed especially for harness racing by crossing Thoroughbreds with Morgans and other breeds.
[From the fact that in order to be registered as a standardbred, a horse originally had to be able to trot a mile within a standard time of two and a half minutes.]