volcanic rock vs lava

volcanic rock and lava both are nouns.

Word	Noun	Adjective	Verb	Adverb
volcanic rock	Yes	No	No	No
lava	Yes	No	No	No

As nouns, lava is a hyponym of volcanic rock; that is, lava is a word with a more specific, narrower meaning than volcanic rock:

volcanic rock: extrusive igneous rock solidified near or on the surface of the Earth
lava: rock that in its molten form (as magma) issues from volcanoes; lava is what magma is called when it reaches the surface

Other hyponyms of volcanic rock include agglomerate, amygdaloid, dacite, basalt, volcanic glass, tufa, tuff.

volcanic rock (noun)	lava (noun)
extrusive igneous rock solidified near or on the surface of the Earth	rock that in its molten form (as magma) issues from volcanoes; lava is what magma is called when it reaches the surface