As the world’s major religions have grown over the centuries, various interpretations and ideological divides have arisen within each one. "Orthodox" is a word often used in reference to religious subgroups, though rarely with much discussion of what it means. In general speech, orthodox means "conventional"--the normal, established way--but when speaking of religion, its usage is a bit narrower.

Religious Orthodoxy

When speaking of religious beliefs, orthodoxy means acceptance of the standard interpretation of a religion as prescribed by a religious authority. Although in common English the opposite of orthodox is unorthodox, religious scholars instead use the term heterodoxy, defined as having beliefs that do not match the official interpretations. Because orthodoxy requires religious specialists who define the correct beliefs, it has mostly only been an issue in organized modern religions. Indeed, it has special meaning in Christianity and Judaism, where Orthodox with a capital "O" refers to specific religious denominations.

Christianity

In Christianity, orthodoxy means agreement with the seven ecumenical councils, meetings held in ancient times to determine the basic beliefs of Christianity. Although the Catholic Church and some Protestant churches are orthodox in this sense, orthodoxy has come to refer to a third branch of orthodox Christianity, also known as the Eastern Orthodox Church. The Orthodox Church and Catholic Church split from each other in the Middle Ages after a series of disagreements over details of Christian belief, as well as clashes regarding whether the Pope should have supreme power over the whole religion.

Judaism

Orthodox Judaism is a broad grouping of Jews who believe it is important to strictly follow their religion’s traditional laws. They consider themselves to be living under the same rules and beliefs established in the time of Moses. Modern Orthodox Jews follow these beliefs by trying to integrate them into modern life, while Haredi or "Ultra-Orthodox" Jews try to stay separate from modern society, believing that no adjustments or new interpretations of the laws are acceptable.

Islam

In Islam, there is no single orthodox denomination, though the concept of orthodoxy is sometimes used when discussing movements to enforce strict interpretations of Muslim Shariah law. Today, there is a growing movement calling for the enforcement of orthodox Islamic law in the Muslim world. In many cases, this involves an opposition to Western culture and support for governments using Shariah as national law.

Other Religions

Use of the term orthodoxy varies when applied to other religions. The most orthodox branch of Buddhism is considered to be Theravada, which has relatively structured and unified teachings and is the main form of the religion in South and Southeast Asia. When speaking of many religions, such as Hinduism, orthodox refers simply to the mainstream beliefs of most followers of the religion, as opposed to the heterodox beliefs of would-be reformers or groups that split off to form other sects.