[ Haha, wow, he sure is grateful for that additional question to answer so he can just focus on that and he doesn't have to address the part about casting one's disciple aside!! ]

Oh, ah, it's the plane of reality where demons live. It's connected to the human realm in a few places but it's more or less just another physical dimension with more aggressive geological conditions and different balances of energy... I take it that isn't something that exists where you come from?