Apartment house

An apartment (American English), flat (British English) or unit (Australian English), is a self-contained housing unit (a type of residential real estate) that occupies only part of a building, generally on a single level. Such a building may be called an apartment building, apartment complex, flat complex, block of flats, tower block, high-rise or, occasionally mansion block (in British English), especially if it consists of many apartments for rent. In Scotland, it is called a block of flats or, if it is a traditional sandstone building, a tenement, which has a pejorative connotation elsewhere. Apartments may be owned by an owner/occupier, by leasehold tenure or rented by tenants (two types of housing tenure).

The term apartment is favored in North America (although in some cities flat is used for a unit which is part of a house containing two or three units, typically one to a floor). In the UK, the term apartment is more usual in professional real estate and architectural circles where otherwise the term flat is used commonly, but not exclusively, for an apartment on a single level (hence a 'flat' apartment). Technically multi-story apartments sometimes referred to as mid-rise apartments and even high-rise apartments when there are many stories. Duplex description can be different depending on the part of the country but generally has two to four dwellings with a door for each and usually two front doors close together but separate - referred to as 'duplex' (or 'triplex') indicating the number of units, not the number of floors as they are usually one story at least in the Texas area.

...
Wikipedia