Horses are one of two extant subspecies of Equus ferus, or the wild horse. It is an odd-toed ungulate mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today. Humans began to domesticate horses around 4000 BC, and their domestication is believed to have been widespread by 3000 BC. Horses in the subspecies caballus are domesticated, although some domesticated populations live in the wild as feral horses. These feral populations are not true wild horses, as this term is used to describe horses that have never been domesticated, such as the endangered Przewalski's horse, a separate subspecies, and the only remaining true wild horse. There is an extensive, specialized vocabulary used to describe equine-related concepts, covering everything from anatomy to life stages, size, colors, markings, breeds, locomotion, and behavior.
Horses' anatomy enables them to make use of speed to escape predators and they have a well-developed sense of balance and a strong fight-or-flight response. Related to this need to flee from predators in the wild is an unusual trait: horses are able to sleep both standing up and lying down. Female horses, called mares, carry their young for approximately 11 months, and a young horse, called a foal, can stand and run shortly following birth. Most domesticated horses begin training under saddle or in harness between the ages of two and four. They reach full adult development by age five, and have an average lifespan of between 25 and 30 years.
Horses could also be found on the planet Tara as well as on Earth. The Fourth Doctor journeyed to this world with his companion, Romana, where they found the terrain to be similar to that of Medieval Europe. Romana encountered Count Grendel, who rode astride a gallant white mustang. 
On The Incredible Hulk, a race horse known as "Rainbow's End" was known for bucking and throwing riders. A horse trainer named Thomas Logan developed a miracle vitamin designed to calm Rainbow's End down. 
Horses were a common mode of transportation in the 31st century reality of the Planet of the Apes television series. Most of the gorilla soldiers seen in the series rode brown horses. General Urko distinguished himself from the others by riding a white horse.
- Bionic Woman: Jaime's Mother - Pony in flashback.
- Isis: The Seeing Eye Horse
- Isis: The Hitchhikers
- Wonder Woman: Death in Disguise - Assassins on horses chase Diana Prince. Wonder Woman uses animal empathy to cause the horses to buck their riders.