In a BDSM relationship, which involves a dominant and a submissive partner, a ponygirl is a submissive female that performs the role of a pony. The term is pretty self-explanatory as to what the ponygirl's obligations are and within such relationships, it represents a form of a power play. As a result, the ponygirl is often called ponygirl BDSM or BDSM pony girl as well.
For sexual purposes, the ponygirls act and dress in the manner of a pony. Although it does not happen all the time, in most situations, the ponygirls are the submissive partners in the Dom/sub relationship. The extent the ponygirls go to are always different depending on their own desires as well as the desires of the dominant, often male partner. Some ponygirls only behave like a pony while others wear items that horses might wear such as bridle and a bit. Some women even accessorize them with fake tails as well in order to properly perform the role of ponygirl.
This activity of behaving in a manner of a pony almost always indicates at least one of the partners has a ponygirl fetish. It does not matter whether it is the dominant or the submissive partner who is a ponygirl fetishist. What matters is that the ponygirl fetish should be executed with the consent of both partners and previously talked about. In case one of the partners feel uncomfortable or highly humiliated, the performance should be stopped immediately.