Generally in the English speaking world a house is self contained dwelling with its own individual entrance from the street. It can be completely separated from neigbourring houses or it can share both walls with its neigbours. A flat is a term more common in the UK and generally means a small apartment in a building. An apartment tends to mean a larger dwelling in a building and is the term more commonly used these days. A room - see your dictionary for this definition - this is easy! A building - any large structure containing apartments, flats, offices et