Horses were domesticated animals used as mounts and beasts of burden on many inhabited worlds in the galaxy.
Horse was the vernacular name for the species used in Basic. The technical term used by scientists was equus. In Ewokese, the species was called "pulga." A small horse was called a "pony" in Basic and a "gaupa" in Ewokese.
An Ewok riding a gaupa rides to slow-down a spooked pulga on the run.
When Cindel Towani was befriended by Wicket after her family crashed on Endor, he showed her an Ewok-made pulga statue, which she identified as a horse. Apparently, at least one world visited by the Towani family in the Galactic Empire had horses.
The Ewoks mainly used small gaupas to ride, but also used large pulgas for heavier loads. In the quest to rescue the Towani parents, most of the Ewoks involved rode gaupas, while Cindel and Wicket traveled in a children-carrying basket aboard a full-sized pulga.
The Force-sensitive witches of Dathomir possessed beautiful black horses, which they sometimes rode instead of Dathomiri rancors. Some of the witches, notably Charal, possessed rings of mysterious (possibly Sith) origin with strange Force "magic" properties that allowed the witches to change the physical shapes of both themselves and their steeds.
A pulga carrying a basket with Cindel Towani inside.
Charal apparently brought her Dathomiri steed with her to the forest moon. To lure Cindel into a trap, she changed her own shape into a beautiful lady, and her horse into a white steed. Apparently, white horses were considered symbolic of purity and nobility in the Galactic Empire.
The Sanyassan Marauders under King Terak also used large horses as mounts. It is possible they brought these steeds with them to the forest moon, as Charal brought her own horse. The Marauders crashed on Endor almost 100 years before the Battle of Yavin, and the horses and ponies used by the Ewoks may well have been descended from Marauder-introduced stock.
Many animals in the Star Wars galaxy resemble horses, but are not. These include four-eared equinoids from Cleroff's World, and numerous species of Naboo: gualaars, guarlaras, and gualamas. Many fans have incorrectly confused Endorian ponies with bordoks.