Any repository for bones, ashes and bodies. The association with such lovely items as the stench of rotting blood is more due to recent literary efforts than the literal meaning of the word. B-grade pulp horror can almost be relied on to use "like a charnel house" to describe some macabre scene that the lack-witted protagonists stumble upon.
Also a publisher of horror fiction. A very thin website is at http://www.charnelhouse.com/