Hot tub, spa, whirlpool, Jacuzzi, jetted bathtub. What do these terms mean? Many people use them interchangeably. Our buyer's guide defines a hot tub as a deep wooden tub and a spa as a shallow, molded acrylic vessel. Both hot tubs and spas share the same hydrotherapy jets, heater, and circulating and filter equipment. The terms whirlpool and jetted bathtub mean the same thing. They are deeper than normal bathtubs and have hydrotherapy jets. Most of them don't have their own heaters, and none of them have a circulating and filter system. A whirlpool or jetted bathtub is usually installed in the bathroom and connected to city sewer and water; you drain the tub when you're done; you can use soap. You don't save water or heat-it all goes down the drain. Jacuzzi is a trade name for a company that manufactures spas and whirl-pool bathtubs; it isn't a special kind of spa. Great Northern® is a registered trade name for our company. We invented the Rubadub Tub® Hot Tub, OpuSpa™ Hot Tub and the Roll-Up® Cover.