Underwater gear is essential for activities such as scuba diving and snorkeling. The two most common pieces of underwater gear are SCUBA and SCUBAS. SCUBA stands for Self-Contained Underwater Breathing Apparatus, and is a device that allows a diver to breathe underwater. SCUBAS stands for Self-Contained Underwater Breathing Apparatus System, and is a system of tanks, regulators, and other equipment that allows a diver to breathe underwater. Both SCUBA and SCUBAS are essential pieces of underwater gear for any diver.