Name and characteristics
In keeping with the Church's teaching on universality and with the Nicene Creed, Orthodox authorities such as Saint Raphael of Brooklyn have insisted that the full name of the church has always included the term "Catholic", as in "Holy Orthodox Catholic Apostolic Church". The official name of the Eastern Orthodox Church is the Orthodox Catholic Church. It is the name by which the church refers to itself in its liturgical or canonical texts, in official publications, and in official contexts or administrative documents. Orthodox teachers refer to the Church as Catholic. This name and longer variants containing "Catholic" are also recognised and referenced in other books and publications by secular or non-Orthodox writers.
The common name of the Church, Eastern Orthodox Church, is a shortened practicality that helps to avoid confusions in casual use. From ancient times through the first millennium, Greek was the most prevalent shared language in the demographic regions where the Byzantine Empire flourished, and Greek, being the language in which the New Testament was written, was the primary liturgical language of the church. For this reason, the eastern churches were sometimes identified as "Greek" (in contrast to the "Roman" or "Latin" church, which used a Latin translation of the Bible), even before the great schism. After 1054, "Greek Orthodox" or "Greek Catholic" marked a church as being in communion with Constantinople, much as "Roman Catholic" did for communion with Rome. This identification with Greek, however, became increasingly confusing with time. Missionaries brought Orthodoxy to many regions without ethnic Greeks, where the Greek language was not spoken. In addition, struggles between Rome and Constantinople to control parts of southeastern Europe resulted in the conversion of some churches to Rome, which then also used "Greek Catholic" to indicate their continued use of the Byzantine rites. Today, many of those same Roman churches remain, while a very large number of Orthodox are not of Greek national origin, and do not use Greek as the language of worship. "Eastern", then, indicates the geographical element in the Church's origin and development, while "Orthodox" indicates the faith, as well as communion with the Ecumenical Patriarchate of Constantinople. There are additional Christian churches in the east that are in communion with neither Rome nor Constantinople, who tend to be distinguished by the category named "Oriental Orthodox". While the Church continues officially to call itself "Catholic", for reasons of universality, the common title of "Eastern Orthodox Church" avoids casual confusion with the Roman Catholic Church.
The first known use of the phrase "the catholic church" (he katholike ekklesia) occurred in a letter written about 110 AD from one Greek church to another (Saint Ignatius of Antioch to the Smyrnaeans) The letter states: "Wheresoever the bishop shall appear, there let the people be, even as where Jesus may be, there is the universal [katholike] Church." Thus, almost from the very beginning, Christians referred to the Church as the "One, Holy, Catholic (from the Greek καθολική, or "according to the whole, universal") and Apostolic Church". The Eastern Orthodox Church claims that it is today the continuation and preservation of that same Church.
A number of other Christian churches also make a similar claim: the Roman Catholic Church, the Anglican Communion, the Assyrian Church and the Oriental Orthodox. In the Eastern Orthodox view, the Assyrians and Orientals left the Orthodox Church in the years following the Third Ecumenical Council of Ephesus (431) and the Fourth Ecumenical Council of Chalcedon (451), respectively, in their refusal to accept those councils' Christological definitions. Similarly, the churches in Rome and Constantinople separated in an event known as the East–West Schism, traditionally dated to the year 1054, although it was more a gradual process than a sudden break. The Church of England separated from the Roman Catholic Church, not directly from the Eastern Orthodox Church, for the first time in the 1530s (and, after a brief reunion in 1555, again finally in 1558). Thus, though it was united to Orthodoxy when established through the work of Saint Augustine of Canterbury in the early 7th century, its separation from Orthodoxy came about indirectly through the See of Rome.
To all these churches, the claim to catholicity (universality, oneness with the ancient church) is important for multiple doctrinal reasons that have more bearing internally in each church than in their relation to the others, now separated in faith. The meaning of holding to a faith that is true is the primary reason why anyone's statement of which church split off from which other has any significance at all; the issues go as deep as the schisms. The depth of this meaning in the Eastern Orthodox Church is registered first in its use of the word "Orthodox" itself, a union of Greek orthos ("straight", "correct", "true", "right") and doxa ("common belief", from the ancient verb δοκέω-δοκῶ which is translated "to believe", "to think", "to consider", "to imagine", "to assume").
The dual meanings of doxa, with "glory" or "glorification" (of God by the Church and of the Church by God), especially in worship, yield the pair "correct belief" and "true worship". Together, these express the core of a fundamental teaching about the inseparability of belief and worship and their role in drawing the Church together with Christ. The Bulgarian and all the Slavic churches use the title Pravoslavie (Cyrillic: Православие), meaning "correctness of glorification", to denote what is in English Orthodoxy, while the Georgians use the title Martlmadidebeli. Several other churches in Europe, Asia, and Africa also came to use Orthodox in their titles, but are still distinct from the Eastern Orthodox Church as described in this article.
The term "Eastern Church" (the geographic east in the East–West Schism) has been used to distinguish it from western Christendom (the geographic West, which at first came to designate the Roman Catholic communion, later also the various Protestant and Anglican branches). "Eastern" is used to indicate that the highest concentrations of the Eastern Orthodox Church presence remain in the eastern part of the Christian world, although it is growing worldwide. Orthodox Christians throughout the world use various ethnic or national jurisdictional titles, or more inclusively, the title "Eastern Orthodox", "Orthodox Catholic", or simply "Orthodox".
What unites Orthodox Christians is the catholic faith as carried through Holy Tradition. That faith is expressed most fundamentally in Scripture and in worship, and the latter most essentially through the Mystery of Baptism and in the Divine Liturgy. The faith lives and breathes by God's energies in communion with the Church. Inter-communion is the litmus test by which all can see that two churches share the same faith; lack of inter-communion (excommunication, literally "out of communion") is the sign of different faiths, even though some central theological points may be shared. The sharing of beliefs can be highly significant, but it is not the full measure of the faith.
The lines of even this test can blur, however, when differences that arise are not due to doctrine, but to recognition of jurisdiction. As the Eastern Orthodox Church has spread into the west and over the world, the church as a whole has yet to sort out all the inter-jurisdictional issues that have arisen in the expansion, leaving some areas of doubt about what is proper church governance. And as in the ancient church persecutions, the aftermath of modern persecutions of Christians in communist nations has left behind both some governance and some faith issues that have yet to be completely resolved.
All members of the Eastern Orthodox Church profess the same faith, regardless of race or nationality, jurisdiction or local custom, or century of birth. Holy Tradition encompasses the understandings and means by which that unity of faith is transmitted across boundaries of time, geography, and culture. It is a continuity that exists only inasmuch as it lives within Christians themselves. It is not static, nor an observation of rules, but rather a sharing of observations that spring both from within and also in keeping with others, even others who lived lives long past. The Holy Spirit maintains the unity and consistency of the Holy Tradition to preserve the integrity of the faith within the Church, as given in the Scriptural promises.
The shared beliefs of Orthodoxy, and its theology, exist within Holy Tradition and cannot be separated from it, for their meaning is not expressed in mere words alone. Doctrine cannot be understood unless it is prayed.  Doctrine must also be lived in order to be prayed, for without action, the prayer is idle and empty, a mere vanity, and therefore the theology of demons. According to these teachings of the ancient church, no superficial belief can ever be orthodox. Similarly, reconciliation and unity are not superficial, but are prayed and lived out.
The Eastern Orthodox Church considers itself to be both orthodox and catholic. Doctrine of Catholicity of the Church, as derived from the Nicene Creed, is essential to Eastern Orthodox Ecclesiology. The term Catholicity of the Church (Greek Καθολικότης τῆς Ἐκκλησίας) is used in its original sense, as a designation for the Universality of the Church, centered around Christ. Therefore, Eastern Orthodox notion of Catholicity is not centered around any singular see, unlike Roman Catholicism, that has one earthly center.
Due to the influence of the Roman Catholic Church in the west, where the English language itself developed, the words "catholic" and "catholicity" are sometimes used to refer to that church specifically. However, the more prominent dictionary sense given for general use is still the one shared by other languages, implying breadth and universality, reflecting comprehensive scope. In a Christian context, the Church, as identified with the original Church founded by Christ and His apostles, is said to be catholic (or universal) in regard to its union with Christ in faith. Just as Christ is indivisible, so are union with Him and faith in Him, whereby the Church is "universal", unseparated, and comprehensive, including all who share that faith. Orthodox Bishop Kallistos Ware has called that "simple Christianity". That is the sense of early and patristic usage wherein the Church usually refers to itself as the "Catholic Church", whose faith is the "Orthodox faith". It is also the sense within the phrase "One, Holy, Catholic, and Apostolic Church", found in the Nicene Creed, and referred to in Orthodox worship, e.g. in the litany of the catechumens in the divine liturgy.
With the mutual excommunications of the East–West Schism in 1054, the churches in Rome and Constantinople each viewed the other as having departed from the true Church, leaving a smaller but still-catholic Church in place. Each retained the "Catholic" part of its title, the "Catholic Church" (or "Roman Catholic Church") on the one hand, and the "Orthodox Catholic Church" on the other, each of which was defined in terms of inter-communion with either Rome or Constantinople. While the Eastern Orthodox Church recognizes what it shares in common with other churches, including the Roman Catholic Church, it sees catholicity in terms of complete union in communion and faith, with the Church throughout all time, and the sharing remains incomplete when not shared fully.