That's not to say that other papal teachings have not been authoritative. Usually a pope's formal teaching is something that is taught infallibly by the ordinary and universal magisterium rather than by virtue of Papal infallibility.
In other words, if the pope says something that has always been clearly Catholic doctrine ("The One True God is the Creator of heaven and earth") it is infallible, not in virtue of papal infallibility, but because he is repeating something which has been ordinarily and universally taught.
Well, at least you know what it means.