A house is a pattern used for habitation by people that generally has walls and a roof to shelter its enclosed space from precipitation, wind, heat, cold, and other elements. Animals including both domestic pets and unwanted animals often live in houses. The word house may also refer to a construction that shelters animals, especially within a zoo. The social unit that dwells in a house is known as a household. Most commonly, a household is a family unit of some kind, though households can be other social groups, such as single persons, or groups of unconnected individuals. Settled agrarian and industrial societies are composed of household units living permanently in housing of various types, according to a selection of forms of Land tenure. English-speaking people generally call any building they routinely occupy home. Many people leave their house during the day for work and activity but typically return to it to sleep or for other activities.