Papal Infallibility is a dogma solemnly defined at the First Vatican Council (1869–1870). Vatican II in Lumen Gentium #25, Canon 749 of the 1983 Code of Canon Law and the Catechism #891 explain the doctrine: “By virtue of his office, the Roman Pontiff possesses infallibility in teaching when as the supreme pastor and teacher of all the Christian faithful, who strengthens his brothers and sisters in the faith, he proclaims by definitive act that a doctrine of faith or morals is to be held.” This charism (gift) of infallibility is exercised only when the Pope issues an ex cathedra statement on faith and morals or when he proposes a teaching united with all the bishops of the world.
Infallibility is not impeccability (being sinless) and it is not inspiration (every word intended and guided by the Holy Spirit). Unlike divine inspiration of scripture, where God directed the sacred authors to write only what He wanted them to write, infallibility merely means there are no moral or doctrinal errors present in the statement. It is true and nothing contradicts what has already been defined as true regarding faith and morals. Papal infallibility means that Catholics believe the pope cannot impose a universal teaching on the faithful which would be false.
It does not mean that every idea or judgment, opinion, or decision of the pope is inspired or always correct. It does not mean the pope cannot personally make mistakes or commit sin, since history has already proved the opposite. Making a mistake is a bad judgment, as to what to say or do, when and how. Infallibility does not affect prudential judgments or even scientific or philosophical knowledge. It merely means that the Holy Spirit guards the Church and the pope in such a way that the pope would be prevented from teaching an error on faith and morals if it were attempted to be imposed upon the universal church.
Whether the pope supported the German or the Italian soccer team in the World Cup has nothing to do with infallibility. His personal opinions on specific military, economic, or political policies are not infallible. Only when he speaks as universal pastor and solemnly defines a moral or doctrinal teaching does extraordinary infallibility occur. Two popes have done that in two thousand years: Pius IX in 1854 when he defined the dogma of the Immaculate Conception and Pius XII in 1950 when he defined the dogma of the Assumption of Mary.
Ordinary papal infallibility is exercised when popes officially teach to the universal Church what has been consistently and perennially taught by previous popes and by bishops around the world united with him. When John Paul II declared in 1994 (Ordinatio Sacerdotalis) that women cannot be ordained or receive the sacrament of Holy Orders, that was an infallible teaching but not an ex cathedra statement. It is just a technical but precise distinction. Ex cathedra statements are part of the extraordinary papal Magisterium. Since only two of these have ever been made so far, that tells you how extraordinary and rare these are. Ordinary papal Magisterium is more frequent and “ordinary” and, as in the case of Ordinatio Sacerdotalis, the content or teaching is infallible but not a specific statement per se. Fallible but official papal teaching does not demand an assent of faith but does require a religious submission of mind and will as explained in Lumen Gentium #25 of the Second Vatican Council and in Canon #752 and #892 of the Catechism.