Some apartment-dwellers own their 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. Apartment building owners, lessors, or managers often use the more general word units to refer to apartments. Units can be used to refer to rental business suites as well as residential apartments. When there is no tenant occupying an apartment, the lessor is said to have a vacancy.

Apartments can be classified into several types. In the US the typical terms are 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, in which one bedroom is separate from the rest of the apartment. Then there are two-bedroom, three-bedroom, etc. apartments. 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. 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.