It's where the stuff that disappears in places like the Bermuda Triangle ends up. The station has been patched together around the place where things "materialise". That effect predates the Worldgates, though it will be linked to the latter.
The majority of inhabitants is human.
It's in some kind of orbit around a star, but it gets considerably less light than Earth. There are no planets in a distance that could be reached from The Junkyard with their own means, though there may be an asteroid belt (undecided).