The Void is a world visited during the Summer's End quest. The Void is a completely empty world found between more well-developed worlds such as Yu'biusk, Gielinor, and Zanaris. It is metaphysically similar to The Abyss, but seems to form the border between The Abyss and other worlds.
During Summer's End, players briefly visit The Void. This part of the void was created when the Spirit Beast began to eat its way through the world borders from the Spirit Realm, into The Abyss, and then into Gielinor.
According to science fiction, 'The Void' is the plane that is in between different universes, in which there is absolutely nothing in there, other than what has been thrown in there.
In theory, the whole of the multiverse is filled with The Void, a lack of existence that, to an inhabitant, would appear to be nothing but an infinite field of white emptiness. The isolated universes within this Void contain far more complex physical laws than the Void itself, including space, time, matter, and energy. Although it is possible for matter to enter the Void and retain its physical existence, there is nothing known to inhabit the Void by nature. These worlds are often, although not always, separated by the Abyss, a border dimension that helps to the worlds to maintain their physical selves.
The void was also mentioned briefly by Azzanadra in a recent Postbag from the Hedge. "I have discovered that many of us have entered the death-sleep, and that Mizzarch, Lamistard and Ralvash were the most recent to face 'the void' in the Ritual." Additionally, after talking to Necrovarus after using the enchanted Amulet of Ghostspeak to release the trapped spirits of Port Phasmatys, when Necrovarus vows to "fry" the player, you respond: "Quiet, evil priest!! If you try anything, I will command you again, but this time it will be to throw yourself into the Endless Void for the rest of eternity." However, whether these refer to The Void as a dimension, or merely are a metaphor for death, remains unclear.