What is "sedevacantism"

n. The belief, held by a minority of Traditionalist Catholics, that the present occupant of the papal see is not the true pope and that the see has been vacant since the 1960s.

Sedevacantism is the position, held by a minority of traditionalist Catholics, that the present occupant of the Holy 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. Sedevacantists believe that there is at present a vacancy of the Holy See that began with John XXIII (1958–63) or at latest with Paul VI (1963–78), who, they say, espoused the heresy of Modernism and otherwise denied solemnly defined Catholic dogmas and so became heretics.

The term "sedevacantism" is derived from the Latin phrase sede vacante, which literally means "with the chair [of St. Peter] vacant". The phrase is commonly used to refer specifically to a vacancy of the Holy See from the death or resignation of a pope to the election of his successor. "Sedevacantism" as a term in English appears to date from the 1980s, though the movement itself is older.

Among those who maintain that the see of Rome, occupied by what they declare to be an illegitimate pope, was really vacant, some have chosen an alternative pope of their own, and thus in their view ended the vacancy of the see, and are known sometimes as " conclavists".

The number of sedevacantists is largely unknown, with estimates given in tens to hundreds of thousands.