I cannot draw that line… even a band can be both… even on an albulm. Take Metallica, their “power ballads” scream ROCK, where as the next track tends to scream METAL. I think though that all metal is rock just as all death/thrash/extreme is metal. I’m an middle aged metalhead, but I’d class punk in the main as a sub class of metal, whereas here it’s under rock. It’s all subjective, even within a band… how many bands have split for musical differences? Some want to soften into rock whereas another band member may want to go more metal. Many bands don’t like the classification at all, so unless we’re looking at the likes of Steel Panther who define themselves, it’s almost impossible to be definitive.

Rock/metal/punk/hardcore/grindcore/death/thrash/heavy rock… call it what you will, may it live forever.