Floating means to lie suspended in a supersaturated saline solution. The high concentration of Epsom salts in the solution allows the body to be completely buoyant; you can freely float on the water without any special breathing technique or muscle contraction. In this zero gravity state all muscle groups can lastingly relax.
A floatation tank is a container or room filled with salt water in which you can experience this state of weightlessness. You lie suspended in a salt water solution, which has the same temperature as the outside surface of the skin (34.8 to 35.2 °C). Inside the tank it is completely dark and silent so that the nervous system and the brain are not stirred by exterior stimuli. This sensory deprivation allows not only for relaxation at a psychological level but also leads to inner, mental peace of mind.