Vista (Q, pron. [ˈvista]) or Wista (pron. [ˈwista]) is a part of the atmosphere that surrounds the world of Arda before the cataclysm at the end of the Second Age. Vista forms the inner layer of normal air: above it is Ilmen, and above that Vaiya.
Vista is the breathable air, with in the top part the clouds, and in the lower parts the paths of birds.