The meaning has shifted since then to describe a state of chaos where all hell has broken loose, but the original, literal definition was " the place where all the demons lived."
And it poured and roared and flashed; and the horses broke loose and ran away; and I fell down, trying to catch them, and hurt my knee, so that I could hardly walk.
And then there's Halloween. In Detroit, October 30 was ruefully known as Devil's Night, a period when all hell would break loose in the form of crime and vandalism.