apartment or flat (British English) or  is a self-contained housing unit (a type of residential real estate) that occupies only part of a building, generally on a single level
What is it called in the united states?
Its called a flat
Thats awesome 
Scotland, it is called a block of flats or, if it is a traditional sandstone 
Are there regulations concerning this?
Not sure yet! In the UK, the term apartment is more usual in professional real estate 
what else can you tell me about this?
There is also the Private equity real estate is a term used in investment finance to refer to a specific subset of the real estate