Harness horses, also known as Standardbreds, are a breed of horse used for harness racing. Pacers are a type of Standardbred that are known for their smooth, lateral gait and are the most common type of horse used in harness racing. Harness horses are trained to pull a two-wheeled cart called a sulky, which is driven by a jockey. Harness horses are bred for speed and endurance, and they are often used in pari-mutuel betting.