Answer:
A Christian denomination is an identifiable religious body under a common name, structure, and doctrine within Christianity.
Over the centuries, Christianity has divided into numerous separate churches and traditions (denominations). Technically, divisions between one group and another are defined by doctrine and church authority. Issues such as the nature of Jesus, the authority of apostolic succession, and papal primacy separate one denomination from another.. Each denomination has its own distinctive beliefs or practices, but they are commonly considered branches of the same religion because they agree on such fundamentals as the Bible, the Trinity, and the teachings of the Nicene Creed. The way in which members regard other denominations varies from mutual respect and acceptance to suspicion and denial that the other group is really "Christian."
The three main branches of Christianity are Catholic, Orthodox and Protestant (some would add Anglican as a fourth). Most of the denominations that exist today developed in the 500 years since the Protestant Reformation and fall under the "Protestant" branch.