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 storey. There are many names for these overall buildings, see below. The housing tenure of apartments also varies considerably, from large-scale public housing, to owner occupancy within what is legally a condominium (strata title or commonhold), to tenants renting from a private landlord (see leasehold estate).
In some countries the word "unit" is a more general term referring to both apartments and rental business suites. The word 'unit' is generally used only in the context of a specific building; e.g., "This building has three units" or "I'm going to rent a unit in this building", but not "I'm going to rent a unit somewhere".
Some buildings can be characterized as 'mixed use buildings', meaning part of the building is for commercial, business, or office use, usually on the first floor or first couple of floors, and one or more apartments are found in the rest of the building, usually on the upper floors.
In England and Wales, some flat owners own shares in the company that owns the freehold of the building as well as holding the flat under a lease. This arrangement is commonly known as a "share of freehold" flat. The freehold company has the right to collect annual ground rents from each of the flat owners in the building. The freeholder can also develop or sell the building, subject to the usual planning and restrictions that might apply. This situation does not happen in Scotland, where long leasehold of residential property was formerly unusual, and is now impossible.
Many campaigners, such as Upton Sinclair and Jacob Riis, pushed for reforms in tenement dwellings. As a result, the New York State Tenement House Act was passed in 1901 to improve the conditions. More improvements followed. In 1949, President Harry S. Truman signed the Housing Act of 1949 to clean slums and reconstruct housing units for the poor.
The Dakota (1884) was one of the first luxury apartment buildings in New York City. The majority, however, remained tenements.