A bronco is a horse that has a tendency to buck, or kick out its rear legs, especially when someone tries to ride it. The term comes from the Spanish language word bronco meaning "rough" or "gruff," which in Mexican usage also describes the horse. It was borrowed and adapted in U.S. cowboy lingo. Broncos were originally wild mustangs, but today most are specially bred to buck. The rodeo events that feature riders trying to stay on bucking broncos are known as "roughstock". In modern English, the "o" is commonly dropped, particularly in the American West, and the animal is simply called a "bronc". The term "bronco" is seldom used for a "wild" or feral horse, because the modern rodeo bucking horse is a domestic animal. Some are specifically bred for bucking ability and raised for the rodeo, while others are spoiled riding horses who have learned to quickly and effectively throw off riders. Informally, the term is often applied in a joking manner to describe any horse that acts up and bucks with or without a rider.