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 without stairs. 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 commonly, but not exclusively, for an apartment without stairs (hence a ‘flat’ apartment). Technically multi-storey apartments are referred to as ‘duplex’ (or ‘triplex’) indicating the number of floors within the property. Usage generally follows the British in Ireland, Singapore, Hong Kong and most Commonwealth nations.
In Malaysian English, flat often denotes a housing block of lesser quality meant for lower-income groups, while apartment is more generic and may also include luxury condominiums. This usage has also been appearing in British English where apartment is used by developers to denote expensive ‘flats’ in exclusive and expensive residential areas in, for example, parts of London such as Belgravia and Hampstead.
Whereas in Japanese English loanwords the term apartment is used for lower-income housing and mansion is used for high-end apartments. However, these both refer to what English-speakers regard as an apartment (or condominium) and not the level of luxury of a mansion when used in English.
In Australian English or New Zealand English, the term flat is traditionally used (although this also applies to any rental property) and more recently the terms unit or apartment are also used.
Tenement law refers to the feudal basis of permanent property such as land or rents. It may be found combined as in “Messuage or Tenement” to encompass all the land, buildings and other assets of a property.
In the United States, some apartment-dwellers own their units, either as co-ops, in which the residents own shares of a corporation that owns the building or development; or in condominiums, whose residents own their apartments and share ownership of the public spaces. Most apartments are in buildings designed for the purpose, but large older houses are sometimes divided into apartments. The word apartment denotes a residential unit or section in a building. In some locations, particularly the United States, the word connotes a rental unit owned by the building owner, and is not typically used for a condominium.
In the 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 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 does not happen in Scotland, where long leasehold of residential property was formerly unusual, and is now not possible.
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”. In Australia, a ‘unit’ refers to flats, apartments or even semi-detached houses. 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.
Source : Wikipedia