The term 'Horse Strap' is a type of equipment used in horse riding. It is also known as a REIN, which is a four-letter word that can be used to solve the crossword. The horse strap is a long, thin strap that is attached to the bridle of the horse and is used by the rider to control the horse's movements. It is usually made of leather or nylon and is adjustable to fit the size of the horse. The horse strap is an essential piece of equipment for any horse rider, as it allows them to control the horse's movements and direct it in the desired direction.