Pony

A pony is by definition any of several different horse breeds with a specific conformation and temperament. They tend to only measure less or equal to 14.2 hands high (hh) at the withers, where one hand is equal to approximately four inches. However, the term "pony" can be used in general (or affectionately) for any small horse, regardless of its actual size or breed.

Ponies and furry
Ponies are quite common for furries that are horse lovers, instead of actual horses. They are generally grouped into the horse crowd. Ponies are typically played by babyfurs and little furs because of their small size and juvenile appearance. Pony characters are also popular among the ponyplay crowd in the fandom. Other popular ponies are the My Little Pony crowd. Dedicated to the popular toy line, fans of My Little Pony collect, draw, even make custom My Little Ponies. Examples of artists and MLP fans include Frisket, HavocFox, Mayra Boyle, Tserisa, Whippetluv, and Doug Winger.

Ponyplay
Main article: Ponyplay. Ponyplay is not limited to the furry fandom and can be a form of erotic sexual role-play (but is not always) where one partner will take on the role of the pony (known as a ponyboy or ponygirl), including appropriate mannerisms and behavior, and the other partner will either act as another pony, or in a sexual context may take the role of rider, trainer or caretaker (or sometimes breeding partner). This type of behaviour normally falls in the BDSM sexual category.

"Ponies" (people involved in ponyplay) generally divide themselves into three groups, although some will participate in two or perhaps all three: Those involved in the heavy BDSM side of ponyplay might utilize an endless array of bit gags, bridles, blinkers (or blinders), saddles, tack (harnesses), pony point trainers, butt plugs with tails, pony boots with "hooves", leashes and collars, BDSM-style "gloves" that prevent use of individual fingers (making a hand more akin to a hoof or paw), and related items are produced and sold commercially to those who wish to act out such fantasies.
 * Cart ponies: usually pulling their owner/trainer in a small horse or pony cart, typically a 2-wheeled vehicle.
 * Riding ponies: used to be ridden, either on all fours or on two legs, with the "rider" on the shoulders of the "pony" (also known as Shoulder riding). Note that a human back is generally not strong enough to take the weight of another adult without risk of injury, so four-legged "riding" is generally symbolic, with the "rider" taking most of their weight on their own legs.
 * Show ponies: just showing off their dressage skills and often elaborate harnesses, plumes and so on.