Vaiya (Q."envelope") referred to the the great Outer Sea ,Outermost Waters (Q."Néni Erúmëar") or "Air" enfolding the world within the Ilurambar or world-walls.It was also called the Celestial or Heavenly Seas and it seemingly was connected to the Heavenly Fields.On their way to Aman Elven ships had to cross first Vista or Vilwa, then Ilmen to finally reach Vaiya.In contrast to Vilwa, which consisted of Vista, air as a substance and Ilmen, the realm of Stars, Vaiya was fully spiritual and incorporeal.
Vaiya was the outermost ocean, beyond even Ekkaia. It was said to be a vast and mystical sea that flowed beneath the world and separated Arda from the Void. In some accounts, Ulmo, Lord of Waters, had dominion over these deep and otherworldly currents. Vaiya was beyond mortal reach and may have been an ocean of the spirit rather than of physical waters.