A nickname informally bestowed upon Pope John Paul II by some liberal Catholic scholars. While more conservative Catholics find this to be downright blasphemous, said scholars protest that it is nothing more than gentle, goodnatured ribbing.
Besides, if you really think about it, the current pope does have a few things in common with R2D2: both are small, hunched over, loved by millions, prone to muttering things in an incomprehensible language, and seem to be impervious to death.