There are planes beyond those scholars commonly indicate.

Beyond the World Axis or the Great Wheel lie planes beyond humanoid reckoning, beyond the even the gods — strange, alien, nightmare realms that birth aberrations.

Collectively, these are the Far Realm. Perhaps they are realms like any other, just so far removed from our experience that we perceive them as malevolent, but whenever they come into contact with the Known Realms, the Far Realm brings corruption and madness. They are a cancer upon the cosmos itself.