An apartment or flat is a self-contained housing unit that occupies only part of a building. Such a building may be called an apartment building, specially if it consists of many apartments for rent. Apartments may be owned by an owner/occupier or rented by tenants
In the UK, some flat owners own a contribute to in the company that owns the freehold of the building. 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 expand or sell the building, subject to the standard planning and boundaries that might apply.
In some countries the word unit is a more general term referring to both apartments and rental business suites. The word is generally used only in the situation of a specific building; When there is no tenant occupying an apartment, the apartment owner or landlord is said to have a vacancy.