The American Quarter Horse, or Quarter Horse, is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other horse breeds in races of a quarter mile or less; some have been clocked at speeds up to 55 mph (88.5 km/h). The American Quarter Horse is the most popular breed in the United States today, and the American Quarter Horse Association is the largest breed registry in the world, with almost 3 million living American Quarter Horses registered in 2014.