Apartments are self-contained residential units occupying part of a larger building. They are usually set out on a single storey of a building and it is for this reason that in some regions (UK, India etc.) they are referred to as "flats". The term apartment is one that is used extensively in Europe, North America and places that use American English. The term "flat" is used in the UK, India and places that use British English. Apartments or flats have their own front door, kitchen, toilet and bathroom. In some countries a 1-bedroom apartment may be advertised as a 1bhk or 1bhk flat. The term "bhk" or "BHK" refers to bedroom, hall and kitchen. This means that the unit would have 1 bedroom, a hall (lounge/sitting room) and kitchen.
Apartments can be found in residential blocks or towers and sometimes as a part of a villa where the floors have been separated each with its own entrance etc.