A random bit of (alleged) storage space. Most of the time they take the form of an extra closet that's big enough to fit at least three people but has no shelves.
They can also be smaller spaces that one must crawl into and around in, once inside.
Guy 1: Dude, this closet is huge, but why doesn't it have anywhere to put stuff? And why is there a tiny door in the back?
Guy 2: Oh, those're just the Jew Holes.