[Inkspot, a while ago] Although using an abbreviation might be classed "cheating" I really cannot find a way to explain the meaning of 3er WG using anything shorter than "communal dwelling shared by three people" in English. WG stands for Wohngemeinschaft, btw. And 3er is not an abbreviation. It's a genetive, of all things.
[Darren, et al, re links] I refer you to this comment I recently made on the subject.