Meaning of "hard core"

[Jo mama]

English Language Tests, Intermediate level

ESL/EFL Test #189 "Idioms - hard", question 3

My parents wouldn't permit me to listen to ......... heavy metal music when I was growing up.

(a) hard core
(b) hard headed
(c) hard cash
(d) hard pressed

English Language Tests, Intermediate level

ESL/EFL Test #189 "Idioms - hard", answer 3

My parents wouldn't permit me to listen to hard core heavy metal music when I was growing up.

Correct answer: (a) hard core
_________________________

what does hard core mean?

Jo mama

[Conchita]

'Hardcore' in the context of heavy metal is a kind of music that has extremely harsh sounds. Heavy metal often has these loud, jarring or discordant notes, which, to many, sound crude and chaotic.