One true church in the context of "Eastern Orthodox Church"

A Christian denomination is a distinct religious body within Christianity that comprises all church congregations of the same kind, identifiable by traits such as a name, particular history, organization, leadership, theological doctrine, worship style and, sometimes, a founder. It is a secular and neutral term, generally used to denote any established Christian church. Unlike a cult or sect, a denomination is usually seen as part of the Christian religious mainstream. Most Christian denominations refer to themselves as churches, whereas some newer ones tend to interchangeably use the terms churches, assemblies, fellowships, etc. Divisions between one group and another are defined by authority and doctrine; issues such as the nature of Jesus, the authority of apostolic succession, biblical hermeneutics, theology, ecclesiology, eschatology, and papal primacy may separate one denomination from another. Groups of denominations—often sharing broadly similar beliefs, practices, and historical ties—are sometimes known as "branches of Christianity". These branches differ in many ways, especially through differences in practices and belief.

Individual denominations vary widely in the degree to which they recognize one another. Several groups say they are the direct and sole authentic successor of the church founded by Jesus Christ in the 1st century AD. Others, however, believe in denominationalism, where some or all Christian groups are legitimate churches of the same religion regardless of their distinguishing labels, beliefs, and practices. Because of this concept, some Christian bodies reject the term "denomination" to describe themselves, to avoid implying equivalence with other churches or denominations.

A Christian denomination is a distinct religious body within Christianity, identified by traits such as a name, organization and doctrine. Individual bodies, however, may use alternative terms to describe themselves, such as church, convention, communion, assembly, house, union, network, or sometimes fellowship. Divisions between one denomination and another are primarily defined by authority and doctrine. Issues regarding the nature of Jesus, Trinitarianism, salvation, the authority of apostolic succession, eschatology, conciliarity, papal supremacy and papal primacy among others may separate one denomination from another. Groups of denominations, often sharing broadly similar beliefs, practices, and historical ties—can be known as "branches of Christianity" or "denominational families" (e.g. Eastern or Western Christianity and their sub-branches). These "denominational families" are often imprecisely also called denominations.

Christian denominations since the 20th century have often involved themselves in ecumenism. Ecumenism refers to efforts among Christian bodies to develop better understandings and closer relationships. It also refers to efforts toward visible unity in the Christian Church, though the terms of visible unity vary for each denomination of Christianity, as certain groups teach they are the one true church, or that they were divinely instituted for the propagation of a certain doctrine. The largest ecumenical organization in Christianity is the World Council of Churches.

In ecclesiology, the Christian Church is what different Christian denominations conceive of as being the true body of Christians or the original institution established by Jesus Christ. "Christian Church" has also been used in academia as a synonym for Christianity, despite the fact that it is composed of multiple churches or denominations, many of which hold a doctrinal claim of being the one true church to the exclusion of the others.

For many Protestant Christians, the Christian Church has two components: the church visible, institutions in which "the Word of God purely preached and listened to, and the sacraments administered according to Christ's institution", as well as the church invisible—all "who are truly saved" (with these beings members of the visible church). In this understanding of the invisible church, "Christian Church" (or catholic Church) does not refer to a particular Christian denomination, but includes all individuals who have been saved. This is in contrast to the one true church applied to a specific concrete Christian institution, a Christian ecclesiological position maintained by the Catholic Church, the Lutheran Churches, the Eastern Orthodox Church, the Oriental Orthodox churches, Assyrian Church of the East, and the Ancient Church of the East. While holding this view, the Lutheran Churches teach that "there are indeed true Christians in other churches" as "other denominations also preach the Word of God, though mixed with error". The branch theory, which is maintained by some Anglicans, holds that those Churches that have preserved apostolic succession are part of the true Church, though the majority of Anglicanism has historically "followed the major continental Reformers in their doctrine of the true church, identifiable by the authentic ministry of word and sacrament, in their rejection of the jurisdiction of the pope, and in their alliance with the civil authority ('the magistrate')".

The term Roman Catholic is sometimes used to differentiate the Catholic Church and its members in full communion with the pope in Rome from other Christians who identify as "Catholic". It is also sometimes used to differentiate adherents to the Latin Church and its use of the Roman Rite from Catholics of the Eastern Catholic Churches. It is not the official name preferred by the Holy See or bishops in full communion with the pope as a designation for their faith or institution.

The term "catholic" is one of the Four Marks of the Church set out in the Nicene Creed, a statement of belief widely accepted across Christian denominations. Catholics, Eastern Orthodox, and Oriental Orthodox consider the term "Catholic" to refer to a single institutional one true church, while Protestant ecclesiology considers it to refer to a church invisible referred to as the Christian Church. The use of "Roman" or "Roman Catholic" to differentiate the Catholic Church dates from the Middle Ages.