An alterreality is a massive universe cluster that contains realitie(s).
Us, Earthlings, are in something called the Earth Dimension, which is 8.719 novemdecillion ly in diameter.
Dimensions have layers: Crust (aka Hyperhelium), with the smallest universes, Upper Mantle (aka Hyperprotium), Lower Mantle (aka Hyperneutronium), Core (aka Visconium), with the larger universes, and the Central Core (aka Dimensiocilium) with the Forostone and the largest universes. We are in the Hyperneutronopause (between Hyperprotium and Hyperneutronium layers of the Earth Dimension. Earth Dimension has between 5 and 425 realities.