The two words are usually not interchangeable. - 바닥: floor (of any kind), ground, bed(of a river, ocean, etc), bottom(밑바닥) - 마루: wood flooring; the planks in such flooring 바닥 is a broad term meaning any kind of floor, but it usually means the flat supporting structure, not the floor's covering layer. It is a widely used term, with usages like 땅바닥(earthen ground), 강바닥(river bed), 시멘트바닥(concrete slab), 방바닥(floor/slab of a room). 마루 originally meant the raised floor made of wood planks. But in modern times it seems to have come to refer to other kinds of floors too, although I'm not sure as to the extent of it. My guess is that for nicely finished floors in a house, office, etc, people may use 마루 to refer to the floor's covering, especially for wood flooring but probably for other kinds too. Other than that it should be 바닥. 바닥 is way more commonly used everyday with expressions like 바닥에 넘어졌다(Fell down on the floor), 바닥에 물 흘리지 마(Don't spill water on the floor), 바닥 모를 추락(fall with no end), etc.

I googled these words and their translation . Are these the words you meant ? 바닥 = floor = the surface of a room or something like car, house etc 마루= flooring = the things used to make the floor eg please take off your shoes when you walk on the floor so that you wont scratched my (wooden) flooring From .Wiki : Flooring is the general term for a permanent covering of a floor, or for the work of installing such a floor covering