As a metalhead, I've been calling things "heavy" for most of my life, but I never really stopped to think about what I meant. It's such an intuitive label to me, with such a clear meaning that neatly translates to the music I'm describing. But these days, stopping to think about what I mean when I talk about music is pretty much my entire job, so I think it's finally time to ask that question: When a metalhead calls a piece of music heavy, what are they actually saying?