The wild horse (Equus ferus) is a species of the genus Equus, which includes as subspecies the modern domesticated horse (Equus ferus caballus) as well as the endangered Przewalski's horse (Equus ferus przewalskii). The European wild horse, also known as the tarpan, that went extinct in the late 19th or early 20th century has previously been classified as a subspecies of wild horse (Equus ferus ferus), but more recent studies have cast doubt on whether those horses were truly wild or if they actually were feral horses or hybrids.

Przewalski's horse had reached the brink of extinction, but was reintroduced successfully into the wild. The tarpan became extinct in the 19th century, but is theorized to have been present on the steppes of Eurasia at the time of domestication. However, other subspecies of Equus ferus may have existed and could have been the stock from which domesticated horses are descended. Since the extinction of the tarpan, attempts have been made to reconstruct its phenotype using domestic horses, resulting in horse breeds such as the Heck horse. However, the genetic makeup and foundation bloodstock of those breeds is substantially derived from domesticated horses, so these breeds possess domesticated traits.

The term "wild horse" is also used colloquially in reference to free-roaming herds of feral horses; for example, the mustang in the United States, and the brumby in Australia. These feral horses are untamed members of the domestic horse subspecies (Equus ferus caballus), not to be confused with the truly "wild" horse subspecies extant into modern times.