The word "unbridled" means something that is not controlled or restrained. It can refer to a person, animal, or object that has no limits and behaves freely without any constraints. The term often implies wildness, passion, or intensity, as in an unbridled desire for success or an unbridled enthusiasm for life. In the context of horses, "unbridled" refers to a horse that is not being ridden with a bridle and therefore runs free without any restraints.