A lot of lore points to the Maw, or at least the mass containing Torghast, having been a realm named Obleron or Obleros. That was likely its name when it was a Covenant realm that Zovaal once likely ruled, and it became his prison when he turned on the other Eternal Ones eons ago. Zovaal, now known as the Jailer, has been pulling dying or stolen realms and adding them to the Maw over the ages.