Papal Infallibility

Infallibility does not mean that the Pope is perfect or never makes mistakes. What it does mean is that when he teaches on matters of faith and morals in his official capacity as chief shepherd of the Catholic Church those teachings are free from error by virtue of the Holy Spirit who "will lead you into all truth" (John 16:13; see also John 14:16-17, 26 and Luke 10:16).  The Pope speaks infallibly when the following conditions are met: 
•    As the visible head of the universal Church
•    To all Catholics
•    On a matter of faith or morals
•    Intending to use his full authority in an un-changeable decision

The Pope speaking infallibly is not a common occurrence and differs from a regular Papal address or homily. The Pope’s intent to use his full authority in an un-changeable decision is always clearly stated and known. Infallibility means that the Church that Christ founded is, by a special Divine assistance, preserved from liability to error in her definitive teachings regarding matters of faith and morals. "The Roman Pontiff, head of the college of bishops, enjoys this infallibility in virtue of his office, when, as supreme pastor and teacher of all the faithful - who confirms his brethren in the faith - he proclaims by a definitive act a doctrine pertaining to faith or morals. . . . The infallibility promised to the Church is also present in the body of bishops when, together with Peter's successor, they exercise the supreme Magisterium, above all in an Ecumenical Council." [Catechism of the Catholic Church no. 891]