A hard plastic or metal shield worn over he penis and testicles, to protect them from impact-related injuries while participating in sports. Usually worn with a special cup-holding jock strap.
Traditional cups were somewhat flat in appearance, without much of a bulge to them. These were often considered to be very uncomfortable to wear. The newer "banana style" cups are curved to conform better to male anatomy, and taper as the go under the balls. The bulge is also a bit more pronounced, to make it more roomy.
Though there are some who don't like the banana style cups, most find them much more comfortable than the traditional style. Banana cups would be especially recommended for a guy with a larger penis and balls.
After getting hit in the groin by that foul ball, Eric was gratefull he was wearing his jock cup. Though it still hurt, he knew it would have been ten times worse if his cock and balls weren't protected.