Had to look up “sedevacantist.”
http://en.wikipedia.org/wiki/Sedevacantism
Sedevacantism is the position, held by a minority of traditionalist Catholics, that the present occupant of the papal see is not truly pope and that, for lack of a valid pope, the see has been vacant since the death of Pope Pius XII in 1958.
I’m just a Protestant, so I try to take a mild approach either way on the issue. I really learned the word because Mel Gibson’s father is a vocal proponent of the idea.