Data source: Gina A. Zurlo and Todd M. Johnson, eds., World Christian Database (Leiden/Boston: Brill, 2024).
| Glossary item | Definition |
|---|---|
| official state languages | Languages proclaimed by states as their official or national means of communication number 114 |
| old age | Usually taken to begin at the age of retirement (60- 65 years). |
| Old Apostolics | Catholic Apostolics (qv), Irvingites. |
| Old Believers | Followers of AD 1666 schisms ex Russian Orthodox Church, retaining use of Old Slavonic; Old Ritualists. |
| Old Calendar | The Old Style or Julian Calendar devised by Julius Caesar in BC 46, now 13 days behind the New or Gregorian Calendar followed by all Orthodox churches up to 1918 and still followed in AD 2000 by (a) the Churches of Jerusalem, Russia, Serbia, and Bulgaria, (b) most of the monasteries on Mount Athos, and (c) various groups of Old Calendarists (qv). |
| Old Calendarists | Also called Paleohemerologites (from Greek, Palaioimerologitai), or Authentic Orthodox; Greek Orthodox who reject the Ecumenical Patriarchate’s change in 1924 from the Old (Julian) Calendar to the New (Gregorian) Calendar. |
| Old Catholics | Followers of schisms ex Church of Rome retaining Old Catholic apostolic succession of bishops; especially schisms of 1702, 1724, 1870, 1897. |
| Old Ritualists | Old Believers (qv). |
| Old Slavic | Church Slavonic (qv). |
| Old Testament | The covenant of God with the Hebrews as set forth in the Bible; or, the 39 canonical books which form its record in the first part of the Bible; or a printed version or copy thereof. |
| old-age population | Persons over 65 years old. |
| older churches | A term sometimes used for the older or historical mainline denominations of Europe and North America, in contrast to the so-called younger churches of the Third World. |
| on trial | Used in Methodist and other circles for new members who are placed on trial for a period of months to demonstrate their commitment to becoming members. |
| on-demand publishing of books | Publication of material which cannot be economically handled conventionally; the production and distribution of copies of books, one or a few at a time, in response to orders rather than from a preprinted stock of copies; usually by photocopying authorprepared copy or production from microform; a recent technique for publishers with ‘excess of material worthy of publication’. |
| Oneness Pentecostals | Denominational Pentecostals originating in the USA from 1910 onwards, now widespread worldwide, who emphasize baptism in the name of ‘Jesus Only’ and who oppose the doctrine of the Trinity. |
| Oneness-Pentecostals | Also termed Unitarian-Pentecostals, Jesus-Only Pentecostals (because of baptism in name of Jesus only). |
| online | Connecting through a network, modem, or high-speed cable to a computer service, usually accessing e-mail or the World Wide Web. |
| on-line database | A large computerized data bank of information arranged for instant retrieval and in which all data can be immediately accessed. |
| Open Brethren | Christian Brethren (qv). |
| open communion | The practice of inviting all adults present at a service of worship, including those from other denominations, to participate in communion at the Lord’s Table. |
| operationalism | The view that the concepts or terms used in non-analytic scientific statements must be definable in terms of identifiable and repeatable operations. |
| operations research | The application of scientific and mathematical methods to the study and analysis of complex problems not traditionally considered to fall within the field of profitable scientific inquiry. |
| ophthalmic mission | A foreign missionary society specializing in eye services. |
| opinion-makers | See decision-makers. |
| opportunity | In evangelization, the occasion, chance, time, or combinations of circumstances, times and places suitable or favorable for persons to hear and understand the gospel. |
Data on 18 categories of religion, including non-religious, by country, province, and people.
Data on all religions, Christian activities, and trends.
Membership data, year begun, and rates of change.
Population and religion data on all major cities & provinces.
Detailed information covering religion, culture, and geography.
A repository of historical data, including a chronology of Christianity from the 1st to 21st centuries.