Literally, the seat is vacant. This is the case when either the Papal chair or an Episcopal see is vant, maning that their chair is vacant. The Papacy has been vacant many times throughout history, the longest prior to 1958 being a little under 3 years. This was ended by locking hte Cardinals in, putting them on bread and water and when this did not work, removing the roof. During a sede vacante of the Papacy, the clergy and faithful are urged to fast and pray for a speedy and unanimous election.
Today this term is also applied to those, who claim that John XXIII, Paul VI and John Paul I were heretical antipopes. These people claim that John Paul II is also an heretical antipope as successor to the above heretics. These people, however, deny the necessity of the Papacy, by failing to end the current sede vacante. This theory has two possible bases:
1. A Pope ceased to be Pope, when he falls into heresy. This, however, cannot be, since a Pope cannot become a heretic.
2. A heretic cannot become a Pope, and since the above were all four heretics prior to their apparent election, then they are not Popes. This is a true statement, based upon the infallible teachings of the Catholic Church.
Literally, the seat is vacant. This is the case when either the Papal chair or an Episcopal see is vant, maning that their chair is vacant. The Papacy has been vacant many times throughout history, the longest prior to 1958 being a little under 3 years. This was ended by locking hte Cardinals in, putting them on bread and water and when this did not work, removing the roof. During a sede vacante of the Papacy, the clergy and faithful are urged to fast and pray for a speedy and unanimous election.