Catholicism is a broad term for describing specific traditions in the Christian churches in theology and doctrine, liturgy, ethics and spirituality.
For many the term usually refers to Christians and churches, western and eastern, in full communion with the Holy See, usually known as the Catholic Church or the Roman Catholic Church. However, many others use the term to refer to other churches with historical continuity from the first millennium.
In the sense of indicating historical continuity of faith and practice, the term "Catholicism" is at times employed to mark a contrast to Protestantism, which tends to look solely to the Bible as interpreted on the principles of the 16th-century Protestant Reformation as its ultimate standard. It was thus used by the Oxford Movement.
For some, however, such as the priest and theologian Richard McBrien, the term refers exclusively and specifically to that "Communion of Catholic Churches" in communion with the Bishop of Rome. In its Letter on Some Aspects of the Church Understood as Communion, the Congregation for the Doctrine of the Faith stressed that the idea of the universal church as a communion of churches must not be presented as meaning that "every particular Church is a subject complete in itself, and that the universal church is the result of a reciprocal recognition on the part of the particular Churches". It insisted that "the universal Church cannot be conceived as the sum of the particular Churches, or as a federation of particular Churches".
According to McBrien, Catholicism is distinguished from other forms of Christianity in its particular understanding and commitment to tradition, the sacraments, the mediation between God, communion, and the See of Rome. According to Orthodox leaders like Bishop Kallistos Ware, the Orthodox Church has these things as well, though the primacy of the See of Rome is only honorific, showing non-jurisdictional respect for the Bishop of Rome as the "first...