“Sensory deprivation tank.” It sounds like a torture device. To be deprived of something certainly has negative connotations, and senses seem pretty essential. Obviously the people who originally named these things were not thinking of marketing opportunities.
Now, most spas that use them call them “float tanks.” I would say this is a far more accurate description of the experience: floating weightlessly, timelessly in empty space. Probably the closest I will ever get to being in actual space, which is sort of what it feels like. In a float tank, you are shut off to sound and light, and there is body-temperature water saturated with epsom salt in the bottom of the tank. The salt makes you buoyant- to the point that you can literally nap in the tank with no worries. Because of the temperature of the water, there is the sensation of “floating” in nothingness. Here are some pictures of the tank.