A hot tub is a large tub or small pool full of heated water and used for hydrotherapy or pleasure. Some have jets for massage purposes. Hot tubs are sometimes also known as spas or by the trade name Jacuzzi.
In contrast to a typical bathtub, a hot tub is designed to be used by more than one person at a time and is usually located outdoors. Also, the water is not changed with each use, but is kept sanitary using methods similar to those used for swimming pool sanitation.