Sedevacantism

Sedevacantism (derived from the Latin words sedes or "seat", and vacans or "vacant")) 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. A tiny number of these claim the vacancy actually goes back to the death of Pope Pius X in 1914.