Pony

A pony is a small horse (Equus ferus caballus). Depending on context, a pony may be a horse that is under an approximate or exact height at the withers, or a small horse with a specific conformation and temperament. There are many different breeds. Compared to other horses, ponies often exhibit thicker manes, tails and overall coat, as well as proportionally shorter legs, wider barrels, heavier bone, thicker necks, and shorter heads with broader foreheads. The word "pony" derives from the old French poulenet, meaning foal, a young, immature horse, but this is not the modern meaning; unlike a horse foal, a pony remains small when fully grown. However, on occasion, people who are unfamiliar with horses may confuse an adult pony with a foal.

http://en.wikipedia.org/wiki/Pony