Personally, a bad album is something I don't desire to listen to again (Lynch Mob's "Smoke This") or has only one song I would choose for a playlist (St. Anger - Frantic) or one that has production and mastering issues; but that's a different discussion. Sure there are all time greats that have a clunker or two in a huge discography or they might have an album or two that gets passed over for better material when I want to listen to that band. But, I don't necessarily think those are bad albums. I guess my list of bands without a bad album would be far too long. Ha.