### Instruction: What is an apartment building?
### Input: Apartment buildings are multi-story buildings where three or more residences are contained within one structure. Such a building may be called an apartment building, apartment complex, flat complex, block of flats, tower block, high-rise or, occasionally, mansion block (in British English), especially if it consists of many apartments for rent. A high-rise apartment building is commonly referred to as a residential tower, apartment tower, or block of flats in Australia.
### Response: An apartment building is a multi-story building with at least three residences. Each residential unit within the building has many different names depending on the country or region; flat is commonly used in British English, while the term apartment is most popular in North America.