As early as 110 AD, Christian scholars used the term "Catholic" to describe the whole Church, because the word itself means universal or whole. St Ignatius of Antioch first wrote using the term catholic for the universal or whole church in 107 A.D. Many other Christian writers followed suit, and used the word to help define the church of the followers of Jesus Christ.
Present day use of the word Catholic
The term "Catholic Church" is usually the informal name of the Roman Catholic Church. The Roman Catholic Church has over one billion members, which about half of Christians in the world. The term "Catholic" is also used in the name of a church or other institution itself, to designate that the Roman Catholic Church supports the institution. The Roman Catholic Church claims that it can basically historically traced to the original Catholic Church. Various groups separated from the basic church over the years.
The Eastern Orthodox Church, Oriental Orthodox Church, and Assyrian Church of the East all claim to also be the one holy catholic church, as does the Roman Catholic Church. These churches do not revere the Pope in Rome in the same way as the Roman Catholic Church does. The Roman Catholic Church believes that the Pope is the successor to St. Peter, and is pastor of the whole church. There are other differences between the Roman Catholic and the other catholic churches. They each have different rules about communion and holy orders, amongst other differences. Recent efforts from both Pope John Paul II and Benedict XVI have encouraged the merging of the Byzantine Church and Roman Catholic churches. These efforts are being made keeping in mind the reluctance of the Byzantine church to become 'Latinized'.