Catholicism has two main ecclesiastical meanings, described in Webster's Dictionary as: a) "the whole orthodox Christian Church or adherence thereto"; and b) "the doctrines or faith of the Roman Catholic Church, or adherence thereto." The term comes from the Greek adjective "katholikos", meaning "general" or "universal".

     A letter that, in 107 AD, Saint Ignatius, Bishop of Antioch wrote to Christians in Smyrna, is the earliest surviving witness to the use of the term "catholic Church" (Smyrnaeans, 8). By it Saint Ignatius designated the Christian Church in its universal aspect, excluding heretics, such as those who "confess not the Eucharist to be the flesh of our Saviour Jesus Christ, which suffered for our sins, and which the Father, of His goodness, raised up again". Yet more explicit was the manner in which Saint Cyril of Jerusalem (circa 315-386) used the term "catholic Church" precisely to distinguish this Church from heretical "Churches". The word "Catholic" has been used ever since to describe the genuine one original Church founded by Christ and the Apostles. The word appears in the main Christian creeds (formal definitions of belief), notably the Apostles' Creed and the Nicene Creed. The Catholic Church, when used not of an abstract invisible entity, but of a visible concrete body of Christians, usually refers to what is also called "the Roman Catholic Church".

     Frequently enough, some members of this Church, especially those of Eastern Rite, apply the term "Roman Catholic Church" not, as in the Church's official documents, to the Church as a whole, but only to its Latin Rite component. Unlike the outsiders just mentioned, they consider communion with the see of Rome essential for all members of the Catholic Church. Catholics administer seven sacraments or "divine mysteries": Baptism, Confirmation, also called Chrismation, Eucharist, Penance and Reconciliation, Anointing of the Sick, Holy Orders and Holy Matrimony.

     The Eastern Orthodox Church and Roman Catholic Church are divided already 951 years. In 1054 Cardinal Humbertus, a representative of Pope Leo IX, and Michael Cerularius, Patriarch of Constantinople, decree each other's excommunication. Some historians look to this act as initiating the Great Schism between the Roman Catholic and Orthodox Christian Churches. To this day each claims to be the One Holy Catholic and Apostolic Church and each denies the other's right to that name.