Old Testament: Also known as the Hebrew Scriptures or Hebrew Bible, the Old Testament makes up the first part of the Christian Bible. Jews do not use this term, and many consider it disrespectful because it implies that the Hebrew Bible is “old” and unnecessary compared with the Christian Scriptures. Use Hebrew Bible in stories solely involving Judaism. It is divided into categories of law, history, poetry and prophecy. All of the books were written before the birth of Jesus. The canonical books used differ among Jews, Protestants, Roman Catholics and Orthodox Christians, although there is much overlap. Old Testament is capitalized in all references. See Apocrypha.

om: In Hinduism, the mantra of the divine. The ancient Sanskrit name for the absolute. All mantras begin with om.

om mani padme hum (OHM MAH-nee PAHD-may HUMM): An important mantra in Tibetan Buddhism, roughly translated as “ (Homage to) the jewel in the lotus.” It honors the Buddha-nature of all beings.

Opus Dei: A Roman Catholic organization founded in 1928 in Madrid by Josemaría Escrívá de Balaguer, who was proclaimed a saint in 2002, to help Catholic laypeople experience God in their daily work. It is not a religious order, although it has priests as members; ninety-eight percent of its members are laypeople. In 1982, Pope John Paul II made it a personal prelature, meaning that it functions a bit like a global diocese, with members of Opus Dei under the authority of a bishop who governs the group. It is formally known as the Prelature of the Holy Cross and Opus Dei. It has been the subject of criticism by former members who found it too authoritarian and by conspiracy theorists who accused it of involvement in right-wing politics in Spain and Latin America. Opus Dei has gained further notoriety in recent years due to its depiction in the popular and controversial novel The Da Vinci Code. Opus Dei is one of what are known as ecclesial movements, that is, grass-roots organizations, usually among laypeople, that transcend parishes and dioceses by attracting members drawn to the movement’s particular focus. These movements have become popular in recent decades. They have often started in Europe but spread internationally. Other well-known ecclesial movements include Communion and Liberation, the Neocatechumenal Way and the Community of Sant’Egidio.

ordination: The process of authorizing a person to perform ministry in an official capacity for a specific religious organization, usually Christian or Jewish. Many denominations require formal education and training, and many ordain deacons as well as clergy. Lowercase ordained and ordination in all references.

Oriental Orthodox Church: A group of Christian churches that includes the Armenian, Indian, Ethiopian, Coptic (Egyptian), Syrian and Eritrean Orthodox churches.

Orisha (oh-REE-shah): In the Santeria religion, it is an emissary of God who rules over human life.

orthodox, orthodoxy: A term used to denote a clear doctrine that implies correct belief according to a particular religion or philosophy. Lowercase except when referring to Judaism or the Eastern branches of Christianity or as part of a denominational name, such as the Orthodox Presbyterian Church.

Orthodox Church: Any of the several Eastern Christian churches that are rooted in the Middle East or Eastern Europe but that do not give allegiance to the Roman Catholic pope. The term Orthodox was adopted by the Eastern Church to signify its adherence to the original apostolic traditions, teachings and style of worship. The Orthodox Eucharistic service is called the Divine Liturgy, and worship is very sensual, involving incense, chants and the veneration of icons. The Roman Catholic and Orthodox churches were united until 1054, when the Great Schism occurred, mainly as a result of disputes over papal authority. The pope in Rome claimed supremacy over the four Eastern patriarchs, while the Eastern patriarchs claimed equality with the pope. Although the split was officially made in 1054, divisions began more than two centuries earlier. Today the spiritual head of Orthodoxy is the ecumenical patriarch of Constantinople, who has no governing authority over the other patriarchs but is called “first among equals.”

Orthodox Church in America: The second-largest body of Orthodox churches in the United States. It traces its origins to the arrival in Kodiak, Alaska, of eight Orthodox missionaries from Russia in 1794. In the early 1960s, the OCA was known as the Russian Orthodox Greek Catholic Church of North America, or The Metropolia. People who joined this group in the 1930s were Eastern Catholics who turned to Orthodoxy after the Vatican forbade them to have married priests in the United States. Today, in addition to the parishes of the former Metropolia, the OCA includes the Romanian Orthodox Episcopate, the Albanian Orthodox Archdiocese and the Bulgarian Orthodox Diocese. In the past two decades the OCA has established more than 220 new parishes, almost all non-ethnic in origin and worshipping only in English. In 1970, the Moscow Patriarchate of the Russian Orthodox Church granted the OCA autonomy, giving it the right to elect its own primate, or presiding hierarch. It has its headquarters in Syosset, N.Y. See Eastern Orthodox.

Orthodox Judaism: The most conservative of the three major branches of Judaism, it strictly adheres to traditional teachings and acceptance of Jewish principles of faith and law. Capitalize in all references. Hasidism is a movement within Orthodox Judaism. See Jewish congregations, Hasidism and Chabad.