An apartment building, block of flats or tenement is a multi-unit dwelling made up of several (generally four or more) apartments (US) or flats (UK). Where the building is a high-rise construction, it is termed a tower block.
A two-unit dwelling is known as a duplex (US) or maisonette (UK); a three-unit dwelling is known as a triplex.
During the 19th century tenements became the predominant type of new housing in Scotland’s industrial cities. (In Northern England, ‘back-to-back’ terraces were more common). Scottish tenements are usually four to six stories in height, with three or four flats on each floor. They are sometimes still referred to as closes or closies (a reference to the passageway through which entry is gained). Stairs and landings are generally designated ‘common areas’, so residents must take it in turns to sweep clean the floors (this rarely happens in practice). Tenement flats are the most common form of accommodation for students who have moved out of University Halls (dorms).
Many multi-storey tower blocks were built in the UK after the Second World War. These are gradually being demolished and replaced with low-rise buildings or housing estates. In Scotland those that remain are usually called simply multis.