Every once in a while I get a entry in my stats that say that the user accessed our site from Facebook with ?ref=rua as a query string — I have looked in all the obvious locations as well as on their documentation:
Nothing seems to show what ?ref=rua refers to.
Any ideas?
it’s the ‘Recently used Apps’ unit which appears on a user’s Timeline (example attached)

By the way, that’s not official documentation you linked to, it’s a third-party site