In Roman Catholicism, a dogmatic definition is an infallible statement published by a pope or an ecumenical council concerning a matter of faith or morals, the belief in which the Catholic Church requires of all Christians (but Christians who are not Catholics do not recognize the Catholic Church's authority in such matters).
Contrary to the stereotype that says that Catholics think everything the pope says is infallible, dogmatic definitions by popes are in fact very rare. Among them are the definition of Pope Pius XII concerning the Assumption of Mary in 1950 and the definition concerning Mary's Immaculate Conception by Pope Pius IX in 1854. Nevertheless, these dogmatic definitions tend to be divisive; anti-ecumenical Protestants say that if Romanist ecumenism was sincere, it would discard them, but the doctrine of Papal infallibility precludes this possibility.
See also