According to Reference.com, a horse is a four-legged, hoofed, herbivorous mammal with long hair on its neck and a long tail of hair. Horses widely in size, color and breed.
About.com explains that horses are categorized under the genus of Equus, which also includes ponies, donkeys and zebras. They evolved from the ancient hyracotherium, which was a very small creature. Eventually, they adapted to life on the plains. Part of this adaptation is seen in their muscular legs and running ability. Their running ability is due in part to their feet, which consist of one hardened toe with the hoof serving as a protective layer. Their long necks make it easy to graze on grass, while their teeth are flat and made for grinding fibrous material. Both the tail and the mane on horses protect them from pests like flies. Horses have an excellent field of vision at almost 360 degrees, which keeps them alert for predators.
According to HowStuffWorks, horses range in size from the diminutive Falabella miniature horse at 30 inches tall and 70 pounds to the massive shire draft horse at 68 inches tall and 2,000 pounds. Quarter horses and thoroughbreds are bred for speed, Arabians are bred for endurance and draft horses are bred for strength. Humans have used horses throughout history as work animals, as transportation and as cavalry in battle.