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.