horse

The horse (Equus ferus caballus) is one of two extant subspecies of Equus ferus. It is an odd-toed ungulate mammal belonging to the taxonomic family Equidae.

Person1: What are those people called that ride horses?
Person2: Equestrians.
Person1: Thanks. I was about to just call them horse-people.
Person2: No, that's a centaur.

Mustang

A Mustang is a free-roaming horse of the Western United States, descended from horses brought to the Americas by the Spanish. Mustangs are often referred to as wild horses, but because they are descended from once-domesticated horses, they are defined as feral horses. The original mustangs were Colonial Spanish horses, but many other breeds and types of horses contributed to the modern mustang, now resulting in varying phenotypes. Some free-roaming horses are relatively unchanged from the original Spanish stock, most strongly represented in the most isolated populations.

Equestrian 1: Oh, that's a nice horse! What's his breed?
Equestrian 2: He is a Kiger Mustang. Got him from Oregon to work on the 100 Day Mustang Challenge with.

Equestrian 1: Aw sweet mate.