The multiverse (or meta-universe, metaverse) is the complete set of all universes and/or planes of existence (including this universe) that together comprise everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them along with supporting mathematical imaginary or non-observing universes. The term, multiverse, was coined in 1895 by the American philosopher and psychologist William James. The Planar Wiki definition reflects views of the Planar Academic Center. The various universes within the multiverse are sometimes called parallel universes.
The structure of the multiverse, the nature of each universe within it and the relationship between the various constituent universes is divided in to two categories: Parallel and Quantum. Parallel universes exist on their own sets of timelines. Within each parallel universe exist an incredible number of off-branching quantum realities that exist (as it were) in a non-observed mathematical state until such a time as an observation from the main parallel trunk universe or an observed universe is made.