The Astral Plane, also known as the Astral Sea, one of the Planes of Existence. It is the space between all planes.
The Astral could be reached from almost any point in the Prime Material Plane or first layer of any Outer plane by spell, psionic ability, or device. It was described as a barren place of other-dimensional nothingness extending in all directions. What little solid substance that floated in the bright, gray void was typically chunks of matter broken off from their original plane. The Astral had no gravity but objects did retain their mass so you could throw small items or push off from large objects to move in the weightless environment.
Time in the Astral flowed at the same rate on a Prime Material plane but the effects of time were slowed almost to a stop―a thousand years in the Astral plane felt like only a day to the traveler. Creatures did not go hungry or age while in the Astral plane. For that reason, its mortal inhabitants needed to return to the Material Plane in order to have children or to reach adulthood.