Antipope

Antipope is a term of the Roman Catholic Church in the context of its official list of popes. An antipope is not included in the list of popes in the Vatican's annual directory, "Annuario Pontificio"
An antipope is a pretender who falsely claims to be pope or who wrongly opposes the legitimate and recognized pope.
The existence or claims of an antipope produces a schism in the Roman Catholic Church. A conflict is caused by those who are opposing the authority of the pope.