A cock ring is a circular sex toy that can go on the base of the penis or on a dildo or butt plug. Alternatively, a penoscrotal ring can go around the base of the penis and the testicles.
Other names for a cock ring are:
penis ring
constriction band
tension ring
A penis becomes erect when chemical messages from the brain cause the arteries in the penis to relax, letting blood flow into it. A cock ring applies pressure to the penis and surrounding areas to trap the blood in the penis for longer. In this way, it helps the penis become firmer and the erection last longer.