In Julian Barbour's book The End of Time: The Next Revolution in Our Understanding of the Universe, Platonia is the name given to his hypothetic entity of a timeless realm containing every possible "Now" or momentary configuration of the universe.
The term can also be applied more generally to the "world of Forms" or "Plato's heaven" in Platonic metaphysics, and to the "ultimate ensemble" in Max Tegmark's variation of multiverse theory.
References
Platonia (philosophy) Wikipedia(Text) CC BY-SA