A tourniquet is a medical device used to control bleeding by applying pressure to a limb. It is typically a band or strap that can be tightened around an arm or leg to restrict blood flow. Tourniquets are often used in emergency situations, such as severe injuries or during surgical procedures, to prevent excessive blood loss. When applying a tourniquet, it is important to place it above the injury site and tighten it until the bleeding stops. Proper use of a tourniquet can be life-saving, but it should only be used when necessary, as prolonged application can cause tissue damage.