Sorrel is a southwestern term for a chestnut horse. The quarter horse
association registers red horses as sorrels. Thoroughbred and Arabian
registries use the term chestnut for all shades of red horses. Purists of
those breeds are sometimes offended by the term sorrel. In general practice,
QH and grades are refered to as sorrels, while other breeds are called
chestnut. You are never wrong in calling a red horse a chestnut, but you may
be wrong in calling it a sorrel.