Belief of the Roman Catholic Church that God protects the pope from error when he speaks about faith or morality WordNet 3.0 & Open English WordNet

Papal infallibility is a dogma of the Catholic Church which states that, in virtue of the promise of Jesus to Peter, the pope when he speaks ex cathedra is preserved from the possibility of error on doctrine "initially given to the apostolic Church and handed down in Scripture and tradition". Wikipedia

Dogma of the Catholic Church; infallibility of certain decisions of the Pope Wikidata

In Catholic theology, the Latin phrase ex cathedra, literally meaning "from the chair", refers to a teaching by the pope that is considered to be made with the intention of invoking infallibility. OmegaWiki

The concept that the Pope, under certain circumstance (when making a statement on faith or morals, etc.) is protected by the Holy Spirit from being able to make a mistake. Wiktionary

Catholic concept of an infallible Pope. Wiktionary (translation)