Subspace

Subspace (also called Negaspace) is a dimension of realspace consisting of absolute nothing, created when the universe first exploded into existence. There are various holes in realspace which lead to subspace, due to various reasons variously speculated by various speculative scientists with varying legitimacy of various speculative degrees.

Some devices have been engineered to rip into subspace as a means of near-instantaneous travel, and many of these devices have been implimented by the Galactic Postal Service.