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.

Koinonia is a transliterated form of the Greek word κοινωνία, which refers to concepts such as fellowship, joint participation, partnership, the share which one has in anything, a gift jointly contributed, a collection, a contribution. In the Politics of Aristotle it is used to mean a community of any size from a single family to a polis. As a polis, it is the Greek for republic or commonwealth. In later Christianity it identifies the idealized state of fellowship and unity that should exist within the Christian church, the Body of Christ. This usage may have been borrowed from the early Epicureans—as it is used by Epicurus' Principal Doctrines 37–38.