A Healing tank is a type of Xel'Naga medical device used to treat a variety of conditions.
Predecessor to a Protoss nurtient tank, the device works by submerging patients in a liquid that stimulates the bodies natural regeneration capabilities (Star Wars: Bacta tank; Dragon Ball Z: Medical Machine). A special nanotech serum is sometimes added to the nutrient compound to increase the rate of healing and purge most known types of diseases.
Hardlight emitters programmed with schematics of a variety of surgical tools are equipped to handle several forms of larger injuries. One of the most used programs is a hardlight cast coupled with a cellular regeneration beam to stimulate the repair of broken limbs (Star Trek - Enterprise: Automated repair station). During times of war, military grade Healing tanks could get critically injured personnel back into fighting form within minutes instead of days.
Some civilian versions appear similar to a personal pool (Beast Wars: Predacon restoration chamber). This allows conscious patients to communicate with others while undergoing treatment. Patients can also speed up their own healing by focusing their psionic powers on injuries.