A half bath is a small bathroom with only a toilet and a sink, as opposed to a full bath with a shower or bathtub. It is also called a powder room or a guest bath.
The term "powder room" originated from the fact that these small rooms were originally used to powder men's wigs in the 17th and 18th centuries, though the rooms did not include toilets or wash bins at the time. Today, half baths provide extra facilities in large houses; they are often located near gathering spaces such as kitchens or living rooms so that guests have a place to use the bathroom without invading the bedrooms. In two-story houses, they are generally situated downstairs.