15 U.S. Code § 8002 - Definitions
The term “ASME/ANSI” as applied to a safety standard means such a standard that is accredited by the American National Standards Institute and published by the American Society of Mechanical Engineers.
The term “barrier” includes a natural or constructed topographical feature that prevents unpermitted access by children to a swimming pool, and, with respect to a hot tub, a lockable cover.
The term “main drain” means a submerged suction outlet typically located at the bottom of a pool or spa to conduct water to a recirculating pump.
The term “safety vacuum release system” means a vacuum release system capable of providing vacuum release at a suction outlet caused by a high vacuum occurrence due to a suction outlet flow blockage.
The term “swimming pool” or “spa” means any outdoor or indoor structure intended for swimming or recreational bathing, including in-ground and above-ground structures, and includes hot tubs, spas, portable spas, and non-portable wading pools.
The term “unblockable drain” means a drain of any size and shape that a human body cannot sufficiently block to create a suction entrapment hazard.
 See References in Text note below.