Unique? I'd say there is only one or two things, since so many of the elements mentioned in other answers are shared with the Orthodox Churches. We all have seven sacraments, transubstantiation, celibacy for bishops, monks and nuns, with other clergy (deacons and priests) either married or celibate, and so on. read more
Catholicism is that religion in which a pope is a sign of its unity and governance. Recent popes have in fact been quite visible world figures. But the pope is an authority who is part of the whole of the Church. read more
The unique features of Catholicism are the 4 marks of the true Church: One. Holy. Catholic (universal). Apostolic. read more