ETYM Cf. French infaillibilité.
The quality of never making an error.
Inability to err in matters of doctrine. In Christianity different beliefs are found. Some believe that only God is infallible, others believe that God, in the person of the Holy Spirit, so guides the church or its leaders that in certain circumstances infallibility is conferred. One tradition is that the church as a whole is infallible, so that doctrines are true if accepted by the whole church.
The first Vatican Council formulated the doctrine that the pope is infallible when speaking on matters of doctrine ex cathedra (“from the throne”, an official, formal pronouncement in his office as pope). It is not meant to imply that the pope’s every utterance is infallible. This doctrine has been the subject of much discussion both within the Roman Catholic Church and with other churches.