According to the teaching of Vatican I, the pope is only infallible when he clearly intends to bind the whole Church in a matter of faith or morals. His everyday pronouncements do not fall under the definition. However, it is also taught that a certain religious submission is due to his pronouncements out of respect for the office, but not if they contradict the faith.
But it is not always clear when something is infallible or not. It is generally agreed that the only two clear exercises of it are the definition of the Immaculate Conception (1854) and of the Assumption of Mary (1950). The definition of papal infallibility was made by the First Vatican Council (1870), so is not considered an exercise of papal infallibility. Many people consider canonizations to be infallible, as it would be impious to believe the Church could venerate as a saint someone who is damned. John Paul II declared in 1994 that the teaching that the Christian priesthood is reserved to males is to be "definitively held by all the faithful," yet this was not regarded as an exercise of papal infallibility, but rather a restatement of a doctrine already infallible by the fact that it has always been taught. Which seems like a hair-splitting difference, and one that also seems to imply that certain doctrines that have been dogmatized were not always taught and believed.