Papal Infallibility is a doctrine of the Roman Catholic Church that asserts the Pope is incapable of error when proclaiming dogma related to faith and morals. This belief is based on the idea that the Pope, as the successor of Saint Peter, is guided by the Holy Spirit in these matters, ensuring that the teachings remain true and consistent. The concept was formally defined during the First Vatican Council in 1870. It applies only under specific conditions, such as when the Pope speaks ex cathedra, or "from the chair," and addresses the entire Church, making it a rare occurrence.