[@Sol Grim]The Origin. -bah dum tsssss-

More seriously, let me explain a little bit. The world, in my head, hasn't really reached a point where it views itself like we view Earth. The people think in terms of nations and continents. The closest to having a full on name for the entire world would be something along the lines of the Mortal World, as compared to the Divine World where the Divines supposedly choose to live now. Perhaps there was a name to the world long ago, maybe there were many but its(they've) been lost thanks to a combination of time and cataclysmic level events.