Avenged sevenfold Rock or metal music?

Me and my brother were arguing about avenged sevenfold. I told him that avenged sevenfold was rock. It says it in iTunes that they are under rock. My brother says I'm stupid and I don't know music. He says they are metal music. Is avenged sevenfold metal or rock? And what's the difference? Like what are some examples or rock and metal music?