What is the equipment used for riding and showing horses called?

The term "tack" refers to the collective equipment used for riding and showing horses. This encompasses a variety of items essential for both the comfort of the horse and the effectiveness of the rider. Tack typically includes a saddle, bridle, girth, stirrups, and other related equipment necessary for training and performance.

Understanding "tack" as a category is important because it represents more than just one piece of equipment, unlike a saddle, which is specific to the seating and riding process, or a bridle, which is used for controlling the horse. Harnesses are generally associated with the use of horses for pulling purposes rather than riding. Therefore, "tack" captures the entirety of riding and showing gear, making it the correct choice in this context.