An apartment (in American English) or flat (in British English) is a self-contained housing unit (a type of residential real estate) that occupies only part of a building. Such a building may be called an apartment building, apartment house (in American English), block of flats, tower block, high-rise or, occasionally mansion block (in British English), especially if it consists of many apartments for rent. Apartments may be owned by an owner/occupier by leasehold tenure or rented by tenants (two types of housing tenure).