flooring vs horizontal surface

flooring and horizontal surface both are nouns.

Word	Noun	Adjective	Verb	Adverb
flooring	Yes	No	No	No
horizontal surface	Yes	No	No	No

As nouns, horizontal surface is a hypernym of flooring; that is, horizontal surface is a word with a broader meaning than flooring:

flooring: the inside lower horizontal surface (as of a room, hallway, tent, or other structure)
horizontal surface: a flat surface at right angles to a plumb line

Other hypernyms of flooring include level.

flooring (noun)	horizontal surface (noun)
the inside lower horizontal surface (as of a room, hallway, tent, or other structure)	a flat surface at right angles to a plumb line
building material used in laying floors