If the universe by definition is 'everything', then what is the rationale for the term coined 'multiverse'. I never quite understood how that came about. Perhaps it is just semantics, but if we want to define 'universe' to mean all that is, then we should not refer to supersets of that. Granted it gets tedious to always say things like 'our observable universe' or 'all space-time that is causally connected'. I think if you allow existence of the concept of potentially disconnected spacetimes, then 'universe' as stated cannot be given the definition of 'all matter and energy' without a little refinement.