The Timeless Void, also called the Outer Dark, the Everlasting Dark or the Ancient Darkness (Q."Avakúma", "Oiakúma", "Kúma") was the dark realm ouside of Arda and the Timeless Halls.It was a region of nonexistence outside Time and Creation where the Essence was absent.
The Void had been there before Eä, which was created within it by Eru.The Void was separated from Ea by the Walls of Night, the only known way in or out of the Void was the Door of Night.
Morgoth had long wandered the Void before he had entered Arda and was banished there by the Valar after the War of Wrath.Ungolianth had been a dweller of the Void he had met and befriended her as well as possibly other Demons of the Void.
See:
Regions
Circles of the World Dark Places Dome of Night Dwellings in the Void Empty Space Gates of the Void Outer Dark Outer Void The Pales Ruamóre
Inhabitants
Demons of the Void Elraukar Shadowfolk Spider-Demons
Inhabitants
Gilthrang Magurgoth Maroch Morgoth Tselakus Ungolianth V'glin