The Astral Plane is the world between worlds, the formless chaos that births universes.
According to various cosmic beings, every universe that has ever existed was birthed from it, and from it, any universe can be reached. At the very least, it extends beyond the Omnilooniverse into other RACC worlds, such as the Patrol Universe and the Raiders Universe.
It looks different to each traveler; Constellation perceived it as black with sparkling gray blobs where it connected to various universes, and this is common for those who don't know what to expect.
It holds the Gateway to Limbo.