Reality is essentially the state of being, as they actually exist.
In terms of Universe's, Multiverse's etc.
One of the theories for a Multiverse is one in which we exist in a much bigger space with 9 spacial dimensions. Another is that our Universe exists in a super-massive black hole slowly pulling us towards the center, and that Multiple realities exist across the event horizon.
Realty itself though may be difficult to fully understand. Areas outside reality could still exist in another form of reality, depending on how one defines it.