A bath (UK English) or bathtub (US English) is a thing people sit in when washing, to wash their body. The bath is usually in the bathroom. A less common name for a bath is a washtub.
Sometimes people will add scents, oils and salts to the bath for better experience.
A bath is also a place where people can sit in water (or other liquids, often hot) for their health. This is where the town name Bath comes from. Public baths for relaxing were built in all parts of the Roman Empire.