According to
Transhumanist Terminology, this is akin to a
Basement Universe, which, briefly, means it's an artificially created
universe linked to another with a
wormhole.
The uses for these are amazing, anything from controlling overpopulation, escape from a dying universe, hiding from your ex-wife, whatever.
The theory seems to have came from some thoughts w/r/t black holes.
Stephen Hawking had a book called Black Holes and Baby Universes.