The term apartment is favored in North America, whereas the term flat is commonly, but not exclusively, used in the United Kingdom, Singapore, Hong Kong and most Commonwealth countries.
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.
In New Zealand English, the two terms are independent: apartment has the US sense, while flat usually refers to any rental property, but especially one shared by students or another non-family group.
Tenement law refers to the feudal basis of permanent property such as land or rents. May be found combined as in "Messuage or Tenement" to encompass all the land, buildings and other assets of a property.
In the US and Canada, some apartment-dwellers own their own apartments, 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 connotes a residential unit or section in a building. In some locations, particularly the United States, the word denotes a rental unit owned by the building owner, and is not typically used for a condominium.
In the UK, some flat owners own a share 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 develop or sell the building, subject to the usual planning and restrictions 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 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 floors, and there are one or more apartments in the rest of the building, usually on the upper floors.
When there is no tenant occupying an apartment, the apartment owner or landlord is said to have a vacancy. For apartment landlords, each vacancy represents a loss of income from rent-paying tenants for the time the apartment is vacant (i.e., unoccupied). Landlords' objectives are often to minimize the vacancy rate for their units. The owner of the apartment, typically when transferring possession to the occupant, gives him/her the key to the apartment entrance and any other keys needed, such as a common key to the building or any other common areas and a mailbox key. When the occupant(s) move out, these keys are typically returned to the owner.
Apartments can be classified into several types. In North America the typical terms are a studio or bachelor apartment (efficiency or bedsit in the UK). These all tend to be the smallest apartments with the cheapest rents in a given area. These kinds of apartment usually consist mainly of a large room which is the living, dining, and bedroom combined. There are usually kitchen facilities as part of this central room, but the bathroom is its own smaller separate room.
Moving up from the bachelors/efficiencies are one-bedroom apartments, in which one bedroom is separate from the rest of the apartment. Then there are two-bedroom, three-bedroom, etc. apartments (Apartments with more than three bedrooms are rare). Small apartments often have only one entrance.
Large apartments often have two entrances, perhaps a door in the front and another in the back. Depending on the building design, the entrance doors may be directly to the outside or to a common area inside, such as a hallway. Depending on location, apartments may be available for rent furnished with furniture or unfurnished into which a tenant usually moves in with their own furniture.