quarter horse, American breed of light horse that originated during the colonial era, partly from Arabian ancestry (see Arabian horse). The name refers to the horse's reputation for speed at the quarter-mile distance. It can spring into full speed and consequently is faster than the Thoroughbred for a short sprint. The breed was by far the most popular cattle horse in the early West. It continues in this role today and is also used almost exclusively for rodeo events such as cutting, roping, and barrel racing. Registered quarter horses are of solid colors, stand 15 to 16 hands (60-64 in./150-160 cm) high, weigh over 1,000 lb (450 kg), and have thick muscular shoulders and short necks.