heavy metal music vs rock

heavy metal music and rock both are nouns.

Word	Noun	Adjective	Verb	Adverb
heavy metal music	Yes	No	No	No
rock	Yes	No	Yes	No

As nouns, rock is a hypernym of heavy metal music; that is, rock is a word with a broader meaning than heavy metal music:

heavy metal music: loud and harsh sounding rock music with a strong beat; lyrics usually involve violent or fantastic imagery
rock: a genre of popular music originating in the 1950s; a blend of black rhythm-and-blues with white country-and-western

Other hypernyms of heavy metal music include rock-and-roll, rock'n'roll, rock 'n' roll, rock and roll, rock music.

heavy metal music (noun)	rock (noun)
loud and harsh sounding rock music with a strong beat; lyrics usually involve violent or fantastic imagery	pitching dangerously to one side
	a genre of popular music originating in the 1950s; a blend of black rhythm-and-blues with white country-and-western
	hard bright-colored stick candy (typically flavored with peppermint)
	a lump or mass of hard consolidated mineral matter
	(figurative) someone who is strong and stable and dependable
	material consisting of the aggregate of minerals like those making up the Earth's crust

heavy metal music (verb)	rock (verb)
	move back and forth or sideways
	cause to move back and forth