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[citation needed]). 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.
In Malaysian English, flat often denotes a housing block of 2 rooms with walk-up, no lift, without facilities, typically 5 storeys tall, and with outdoor parking space, 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.
In Japanese English loanwords, the term apartment is used for lower-income housing and mansion is used for high-end apartments; but both terms refer to what English-speakers regard as an apartment (or condominium) and not the level of luxury of a mansion in English parlance.