flux density vs density

flux density and density both are nouns.

Word	Noun	Adjective	Verb	Adverb
flux density	Yes	No	No	No
density	Yes	No	No	No

As nouns, density is a hypernym of flux density; that is, density is a word with a broader meaning than flux density:

flux density: (physics) the number of changes in energy flow across a given surface per unit area
density: the amount per unit size

Other hypernyms of flux density include denseness.

flux density (noun)	density (noun)
(physics) the number of changes in energy flow across a given surface per unit area	the amount per unit size
	the spatial property of being crowded together