In medieval theatre, a hellmouth was a prop or mechanical device which was used to attempt to scare the audience by vividly dramatizing an entrance to Hellhttp://skew.ot.com/eleven/hellmouth.html. In Roman church history, the concept of Leviathan (translated from Hebrew, Job 41:1, "wreathed animal") has been equated with this description, although there is no etymological basis for this equation.

Welcome to the Hellmouth - S1 - A “center of mystical energies” which draws demons to it.

a portal, a gate that links the underworld to our world

a pool of energy