The term "apartment" is favored in North America, whereas the term "flat" is sometimes, but not exclusively, used in the United Kingdom and most other English-speaking areas and 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.
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.
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."
When there is no tenant occupying an apartment, the lessor is said to have a vacancy. For apartment lessors, each vacancy represents a loss of income from rent-paying tenants for the time the apartment is vacant (i.e., unoccupied). Lessors' objectives are often to minimize the vacancy rate for their units. The owner of the apartment typically when transferring possession to the occupant(s) gives him/her the key to the apartment entrance door(s) and any other keys needed to live there, such as a common key to the building or any other common areas, and an individual unit mailbox key. When the occupant(s) move out, these keys are typically returned to the owner.
Apartments can be classified into several types. One is a Studio, efficiency, bedsit, or bachelor style apartment. 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 efficiencies are one-bedroom apartments where one bedroom is a separate room from the rest of the apartment. Then there are two-bedroom, three-bedroom, etc. apartments. Small apartments often have only one entrance/exit.
Large apartments often have two entrances/exits, perhaps a door in the front and another in the back. Depending on the building design, the entrance/exit 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. A garden apartment has some characteristics of a townhouse: each apartment has its own entrance, and apartments are not placed vertically over one another. However, a garden apartment is usually only one story high and never more than two stories; they are often one-bedrooms and almost never more than two-bedrooms. Some garden apartment buildings place a one-car garage under each apartment, with pedestrian entrances from a common courtyard open at one end. The grounds are more landscaped than for other modestly scaled apartments. (Alternately, "garden apartment" can refer to a unit built half below grade, putting its windows at garden level.}
Laundry facilities may be found in a common area accessible to all the tenants in the building, or each apartment may have its own facilities. Depending on when the building was built and the design of the building, utilities such as water, heating, and electricity may be common for all the apartments in the building or separate for each apartment and billed separately to each tenant (however, many areas in the US have ruled it illegal to split a water bill among all the tenants, especially if a pool is on the premises). Outlets for connection to telephones are typically included in apartments. Telephone service is optional and is practically always billed separately from the rent payments. Cable television and similar amenities are extra also. Parking space(s), air conditioner, and extra storage space may or may not be included with an apartment. Rental leases often limit the maximum number of people who can reside in each apartment. On or around the ground floor of the apartment building, a series of mailboxes are typically kept in a location accessible to the public and, thus, to the mailman too. Every unit typically gets its own mailbox with individual keys to it. Some very large apartment buildings with a full-time staff may take mail from the mailman and provide mail-sorting service. Near the mailboxes or some other location accessible by outsiders, there may be a buzzer (equivalent to a doorbell) for each individual unit. In smaller apartment buildings such as two- or three-flats, or even four-flats, garbage is often disposed of in trash containers similar to those used at houses. In larger buildings, garbage is often collected in a common trash bin or Dumpster. For cleanliness or minimizing noise, many lessors will place restrictions on tenants regarding keeping pets in an apartment.
In some parts of the world, the word apartment refers to a new purpose-built self-contained residential unit in a building, whereas the word flat means a converted self-contained unit in an older building. An industrial, warehouse, or commercial space converted to an apartment is commonly called a loft.
When part of a house is converted for the ostensible use of a landlord's family member, the unit may be known as an in-law apartment or granny flat, though these (sometimes illegally) created units are often occupied by ordinary renters rather than family members. In Canada these suites are commonly located in the basements of houses and are therefore normally called basement suites or "mother-in-law suites."
In Milwaukee vernacular architecture, a Polish flat is an existing small house or cottage that has been lifted up to accommodate the creation of a new basement floor housing a separate apartment, then set down again; thus becoming a modest two-story flat.
In Russia, a communal apartment («коммуналка») is a room with a shared kitchen and bath. A typical arrangement is a cluster of five or so apartments with their common kitchen and bathroom and their own front door, occupying a floor in a pre-Revolutionary mansions. Traditionally a room is owned by the government and assigned to a family on a semi-permanent basis. It is possible to "privatize" a room by paying a large sum of money to the government; then it can legally be sold.