The term 'Jock Strap' is a type of athletic support garment worn by athletes to provide support and protection for the groin area. The term 'REIN' is a four-letter word that can be used to describe the straps of the jock strap, which are used to secure it in place. The straps of the jock strap are often referred to as 'REINS' because they help to keep the garment in place and provide support to the athlete.