Papal infallibility means that under certain conditions the Roman Pontiff (the Pope) cannot err when teaching about faith or morals. This is called speaking ex cathedra and its conditions include:
The Pope must speak as the pastor and teacher of all Christians (cum omnium Christianorun pastoris et doctoris munere fungens).
The teaching must define a doctrine of faith or morals (doctrinam de fide vel moribus).
The doctrine must be accepted by the universal Church (universa Ecclesia tenendam).
The Roman Pontiff must define the proposed doctrine for acceptance by the whole Church (definitive actu proclamat).
Whether any ex cathedra statements exist is debatable. The Immaculate Conception and the Assumption have been cited as ex cathedra statements. Regardless, the Church attempted to cover this nonsense with Canon Law 749 § 3, which states:
No doctrine is understood as defined infallibly unless this is manifestly evident.
To be true, a doctrine must first be declared infallible before its infallibility is manifestly evident, which is circular reasoning.
