An apartment is a self-contained housing unit that occupies only part of a building. Apartments may be owned (by an owner/occupier) or rented (by tenants).

A common alternative term for apartment is flat. The term apartment is favored in North America, whereas the term flat is commonly, but not exclusively, used in the United Kingdom, Ireland and the 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.