| OpenNAP | Operating system | Open content |
| OperatorThis article is about operators in mathematics, for other kinds of operators see operator (disambiguation). In mathematics, an operator is some kind of function; if it comes with a specified type of operand as function domain, it is no more than another w | Open sourceNote: "open source" in the intelligence community simply means "any information accessible to the public, possibly after paying a fee". This article is about open source software, a more common meaning for the term "open source". Open source or open sourc | OpelOpel originally and more correctly known as Adam Opel AG is an automobile maker in Germany, since 1929 part of General Motors. As Opel started to build cars, it also made household goods. It opened for business on January 21, 1899. Many cars sold by Gener |
| Optical telegraphThe optical telegraph preceded the electrical telegraph. It was faster than riding couriers for bringing a message over long distances. Types of optical telegraph are the semaphore, ship flags, smoke signals, and beacons. The distance that an optical tele | Open-source licenseAn open-source license is a copyright license for computer software that makes the source code available under terms that allow for modification and royalty-free redistribution. One popular (and sometimes considered normative) set of open source licenses | Open Source DefinitionThe Open Source Definition is used by the Open Source Initiative to determine whether or not a software license can be considered open source. The definition was based on the Debian Free Software Guidelines, written and adapted primarily by Bruce Perens. |
| Open Source InitiativeThe Open Source Initiative is an organization dedicated to promoting open source software. It was founded in February 1998 by Bruce Perens and Eric S. Background In 1997, Eric S. Raymond presented his revolutionary paper on software engineering, The Cathe | Operation SealionOperation Sealion Unternehmen Seelowe in German) was a World War II German plan to invade Britain. It was never carried out. Preparations began after the Fall of France, when the Germans felt they had already won the war. Britain, however, refused to star | OperaCharles Garnier's Opera, Paris, opened 1875 Opera is an art form consisting of a dramatic stage performance set to music. The drama is presented using the typical elements of theater such as scenery, costumes, and acting. However, the words of the opera, |
| OpenBSD | Optical fiber | Opera (browser) |
| Optimization | Open Directory Project | Open-wheeler |
| Ophiuchus | Optics | Optical isomerism |
| OpenGL | Operating system advocacy | OpenSSH |
| Optical brightener | Operation Barbarossa | Operand |
| Opole Voivodship | Open cluster | Operator overloading |
| Opium | Opiate | Operation Enduring Freedom |
| Operation Deadlight | Open source movement | Optic neuritis |
| Open Skies Treaty | Operation El Dorado Canyon | Operational amplifier |
| OpenVMS | Openlaw | Opencola |
| Open Source Technology Group | Optical depth | Open system (computing) |
| Operetta | Open set | Optical rotation |
| Open systems interconnect | Optatam Totius | Optical amplifier |
| Open network architecture | Open systems architecture | Open Systems Interconnection Specification |
| Operation | Optical attenuator | Optical axis |
| Optical density | Optical disc | Optical isolator |
| Optical path length | Optical power budget | Optical power margin |
| Optical spectrum | Optical switch | Optical time domain reflectometer |
| Open content movement | Operation Anaconda | Optical phenomenon |
| Open mail relay | Open Shortest Path First | Operations research |
| Open Source Software | Opportunity cost | Optima |
| Opeth | Opossum | Optical astronomy |
| Optical character recognition | Opera buffa | Optimization (mathematics) |
| Open Translation Engine | OpenStep | Optical illusion |
| Opal | Ophthalmology | Operation Market Garden |
| Opera Australia | Operation Fortitude | Oprah |
| Oprah Winfrey | Optic chiasm | Operational definition |
| Operation TIPS | Operation Entebbe | Opus |
| OpenOffice.org | Open-sourcing | Ophrah |
| Ophir | Ophel | Operation Torch |
| Ophelia (moon) | Opole | Ophion |
