A covering for the face, intended to be worn while in the water. Diving masks, also called "swim masks", usually cover the eyes and nose, and seal securely to the face so water doesn't leak in, trapping a pocket of air next to the face. Jeez, is it pitch black in there? No, because a diving mask will have a large lens or window in front made of glass or some other transparent material. By keeping water out of the eyes, a diving mask allows the wearer to see underwater things clearly, without the blurriness that would be present if one just opens one's eyes underwater. As the name suggests, diving masks are worn while scuba diving. They are also worn while snorkeling, or anytime someone wants to see things really well underwater.