A trotter horse is a type of horse specifically bred and trained to perform the trotting gait, a two-beat diagonal gait commonly used in harness racing where the horse pulls a sulky or cart. These horses are typically medium-sized, stand around 15.1 to 16.3 hands high, and have a balanced conformation with sloped shoulders, long limbs, and powerful hindquarters for speed and endurance. Examples include the French Trotter and the Irish Standardbred Trotter, known for their stamina and athleticism.