Definition of first floor noun from the Oxford Advanced Learner's Dictionary

first floor

noun
 
;
 
usually the first floor [singular]
 
1 (British English) the level of a building above the ground levelMenswear is on the first floor.2 (North American English) (British English ground floor) the floor of a building that is at the same level as the ground outsidefirst-floor
 
;
 
adjective [only before noun]a first-floor flat/apartment
Usage noteUsage note: floorIn British English the floor of a building at street level is the ground floor, the one above it is the first floor and the one below it is the basement, or lower ground floor in a public building.In North American English the floor at street level is usually called the first floor, the one above it is the second floor and the one below it is the basement. In public buildings the floor at street level can also be called the ground floor. note at storey