A half bath is a term used by real estate agents when valuing property. It contains both a sink and toilet, but no shower or bath. It can be larger than your full bathroom and still only be considered a half bath if it has no shower or tub. They are common in houses with large families to reduce the morning queue for the toilet. Generally, they are on a different floor to the main bathroom. If your main bathroom is upstairs, then a half bath would be downstairs.