Roman Catholicism is the entirety of the beliefs and practices of the Western and Eastern churches which are in full communion with the Pope of Rome as the claimed successor of St. Peter the Apostle, united together as the Catholic Church. The term Roman Catholic was defined by the Roman Emperor Theodosius on February 27 AD 380 in the Theodosian Code XVI.i.2: "It is our desire that all the various nations which are subject to our clemency and moderation, should continue the profession of that religion which was delivered to the Romans by the divine Apostle Peter, as it has been preserved by faithful tradition and which is now professed by the Pontiff Damasus and by Peter, Bishop of Alexandria, a man of apostolic holiness. According to the apostolic teaching and the doctrine of the Gospel, let us believe in the one Deity of the Father, Son and Holy Spirit, in equal majesty and in a holy Trinity. We authorize the followers of this law to assume the title Roman Catholic Christians; but as for the others, since in our judgment they are foolish madmen, we decree that they shall be branded with the ignominious name of heretics, and shall not presume to give their conventicles the name of churches. They will suffer in the first place the chastisement of divine condemnation and the second the punishment of our authority, in accordance with the will of heaven shall decide to inflict."
[Extract of English translation from Henry Bettenson, ed., Documents of the Christian Church (London: Oxford University Press, 1943), p. 31, cited at Medieval Sourcebook: Theodosian Code XVI by Paul Halsall, Fordham University. Retrieved Jan 5, 2007. The full Latin text of the code is at IMPERATORIS THEODOSIANI CODEX Liber Decimus Sextus (170KB download), archived from George Mason University. trieved Jan 5, 2007.]