Open University The Open University is the UK's 'open' learning university, established in 1969. The majority of students are based in the United Kingdom , but its courses are also studied in the rest of Europe, in Africa and the Far East. The administration is based at Walton Hall, Milton Keynes , Milton Keynes in Buckinghamshire, but has offices in each of its thirteen regions around the UK.
	Open-end fund An open-end(ed) fund is a Collective investment scheme which can issue and redeem shares at any time. An investor can purchase shares in such funds directly from the mutual fund company, or through a stock broker house. Open-ended funds are available in most developed countries, however terminology and operating rules vary.
	Opera Opera is a drama art form, originating in Italy, in which the emotional content or primary entertainment is conveyed to the audience as much through music, both vocal and instrumental, as it is through the lyrics. From the beginning of the form , there has been contention whether the music is paramount, or the words, a theme that Richard Strauss took up in his final opera, Capriccio .
	Operating system An operating system is a software program that manages the Computer hardware and software resources of a computer. A key component of system software, the OS performs basic tasks, such as controlling and allocating memory, prioritizing the processing of instructions, controlling input and output devices, facilitating networking, and managing files.
	Operating theatre An operating theatre or operating room is a room within a hospital within which surgery operations are carried out. Operating theatres were so-called in the United Kingdom because they traditionally consisted of semi-circular amphitheatres to allow students to observe the medical procedures.
	Operon An operon is a group of key nucleotide sequences including an operator, a common promoter, and one or more structural genes that are controlled as a unit to produce mRNA. Operons occur primarily in prokaryotes and nematodes. They were first described by Franois Jacob and Jacques Monod in 1961.
	Opheodrys Opheodrys is a genus of small colubrid snakes commonly referred to as green snakes. The genus consists of two distinct species with five recognized subspecies.
	Opheodrys aestivus The Rough Green Snake is a non-venom North American snake. It is sometimes Grass Snake or Green Grass Snake, but these names are more commonly applied to the Smooth Green Snake, Opheodrys vernalis. The Rough Green Snake is docile, often allowing close approach by humans, and seldom, if ever, bites.
	Ophidiidae The Ophidiidae, including the cusk eels, are a group of marine fishes in the order Ophidiiformes. The name is from Greek language ophis meaning "snake", and refers to their eel-like appearance. However, they can be distinguished from true eels by their ventral fins, which are developed into a forked Barbel-like organ below the mouth.
	Ophioglossaceae Ophioglossaceae is a family of primitive ferns, currently thought to be most closely related to Psilotum, the two together forming the Cladistics to the rest of the ferns. The number of genera included in the family varies between different authors' treatments, and most conservatively the family is treated as containing three genera, Ophioglossum, Botrychium, and Helminthostachys.
	Ophioglossum Ophioglossum is a genus of about 25-30 species of Ophioglossales in the family Ophioglossaceae, with a cosmopolitan but primarily tropical and subtropical distribution. The name Ophioglossum comes form the Greek language, and means "snake-tongue".
	Ophiuchus Ophiuchus is one of the 88 constellations, and was also one of the 48 listed by Ptolemy. Of the 13 zodiac constellations , Ophiuchus is the only one which is not counted as an astrological sign — see below for more information. Ophiuchus is depicted as a man supporting a Serpens; the interposition of his body divides the snake into two parts, Serpens Caput and Serpens Cauda, which are nonetheless counted as one constellation.
	Ophrys The genus Ophrys is a large group of orchids from the alliance Orchis in the subtribe Orchidinae. There are many natural hybrids. The type species is Ophrys insectifera L.1753 They are referred to as the "Bee orchids" due to the flowers of some species resemblance to the furry bodies of Bumble Bees and other insects.
	Ophthalmia neonatorum Ophthalmia neonatorum is a form of conjunctivitis contracted by newborns during delivery. The baby's eyes are contaminated during passage through the birth canal from a mother infected with either Neisseria gonorrhoeae or Chlamydia trachomatis.
	Ophthalmology Ophthalmology is the branch of medicine which deals with the diseases and surgery of the visual pathways, including the eye and brain. The word ophthalmology comes from the Greek language roots ophthalmos meaning eye and logos meaning word; ophthalmology literally means "The science of eyes." As a discipline it applies to animal eyes also, since the differences from human practice are surprisingly minor and are related mainly to differences in anatomy or prevalence, not differences in disease pro
	Opiliones The Phalangids or Opiliones are eight-legged invertebrate animals belonging to the order Opiliones in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda. As of 2005, over 6,300 species of Phalangids have been described worldwide. The order Opiliones can be divided in four suborders: Cyphophthalmi, Eupnoi, Dyspnoi and Laniatores.
	Opisthobranchia In zoology, the Opisthobranchia used to be a Subclass of Gastropoda , within the phylum Mollusca, but they are now treated as an Scientific classification. They are highly evolved gastropods, characterised by a single gill behind the heart, from which the subclass derives its name and two pairs of tentacles.
	Opium Opium, or opum is a narcotic analgesic Medication which is obtained from the unripe seed pods of the opium poppy .
	Opium den An opium den is an establishment where opium is sold and consumed. Opium dens were prevalent in many parts of the world in the nineteenth century. In the west they were frequented by and associated with the Chinese. Patrons were seen reclining and smoking opium out of special pipes.
	Opium poppy The opium poppy, Papaver somniferum, is the type of poppy from which opium and all refined opiates such as morphine are extracted, as well as an important food item. There are many varieties of this poppy species. Colors of the flower vary widely, as do other physical characteristics.
	Oppenheimer Oppenheimer may be the surname of: * Alan Oppenheimer, a film actor * David Oppenheimer, a mayor of Vancouver, British Columbia * Andrs Oppenheimer, an Argentinian author and journalist known for his analysis of Latin American politics. * Ernest Oppenheimer, founder of a producers' cooperative & single channel marketing, the forerunner of De Beers
	Opsin Opsins are a group of light-sensitive 35-55 kDa membrane bound G protein-coupled receptors found in photoreceptor cells of the retina. They are involved in vision, mediating the conversion of a photon of light into an electrochemical signal, the first step in the visual transduction cascade.
	Optic chiasm The optic chiasm is the part of the brain where the optic nerves partially cross. Specifically, the nerves connected to the right eye that attend to the right visual field cross with the nerves from the left eye that attend to the left visual field. The parts of both eyes that attend to the right visual field are processed in the left visual system in the brain, and vice versa.
	Optic disc The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive photoreceptor to respond to a light stimulus at this point thus it is also known as "the blind spot" or "anatomical blind spot"; the break in the visual field created by the optic disc is also called "blind spot" or "physiological blind spot".
	Optic nerve The optic nerve, also called cranial nerve II, is the nerve that transmits visual information from the retina to the brain.
	Optic tract The optic tract is a part of the visual system in the brain. It is a continuation of the optic nerve and runs from the optic chiasm to the lateral geniculate nucleus. The right optic tract consists of temporal retinal fibers from the right eye and nasal retinal fibers from the left eye; conversely, the left optic tract consists of temporal retinal fibers from the left eye and nasal retinal fibers from the right eye.
	Optical disc In computing, sound reproduction, and video, an optical disc is flat, circular, usually polycarbonate disc whereon data is stored in the form of pits within a flat surface. This data is generally accessed when a special material on the disc is illuminated with a laser diode.
	Optical fiber An optical fiber or fibre is a thin, transparency fiber, usually made of glass or plastic, for transmitting light. Fiber optics is the branch of applied science and engineering concerned with such optical fibers. Optical fibers are commonly used in telecommunication systems, as well as in lighting, sensors, and image-forming optical system.
	Optical illusion An optical illusion characterized by visual perception images that, at least in common sense terms, are deceptive or misleading. Therefore, the information gathered by the eye is processed by the brain to give, on the face of it, a percept that does not tally with a physical measurement of the stimulus source.
	Optical phenomenon An optical phenomenon is any observable event which results from the interaction of light and matter. See also list of optical topics and optics. Common optical phenomena are often due to the interaction of light from the sun or moon with the atmosphere, clouds, water, or dust and other particulates.
	Optical telescope An optical telescope is a telescope which is used to gather, and lens light, for directly viewing a magnification image, making a photograph, etc. The term is used especially for a monocular with static mounting for observing the sky. Handheld binoculars are common for other purposes.
	Optics Optics is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. Optics explains optical phenomenon. The field of optics usually describes the behavior of optical spectrum, infrared, and ultraviolet light; however because light is an electromagnetic wave, analogous phenomena occur in X-rays, microwaves, radio waves, and other forms of electromagnetic radiation.
	Optimism Optimism, the opposite of pessimism, exemplifies a World view where one looks upon the world as a positive place. Optimists generally believe that people and events are inherently Goodness and value theory. They have a so-called "positive" outlook on personal life , believing that things will work out in the end.
	Option In finance, an option is a contract whereby one party has the right but not the obligation to exercise a feature of the contract on or before a future date. The other party has the obligation to honor the specified feature of the contract. Since the option gives the buyer a right and the seller an obligation, the buyer has received something of value.
	Optometry Optometry is the health profession concerned with examination, diagnosis, and treatment of the eyes and related structures and with determination and correction of vision problems using lens and other optical aids .
	Opuntia Opuntia is a genus in the cactus family Cactus. Both prickly pears and chollas are included in this genus of about 250 species distributed throughout most of the New World. The biological type of the genus is the Indian Fig Opuntia Opuntia ficus-indica.
	OR gate The OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are HIGH (1). If neither input is HIGH, a LOW output (0) results.
	Oral contraceptive Oral contraceptives are chemicals taken by mouth to inhibit normal fertility. All act on the hormone system. Oral contraceptives have been on the market since 1960, and enjoy great popularity. They are used by millions of women around the world, but usage prevalence varies: one quarter of reproductive age women in the United Kingdom take the pill,
	Oral Roberts Oral Roberts is an United States Pentecostal televangelist. He is also a leader in the charismatic movement.
	Oral sex Oral sex consists of all the Human sexual behavior that involve the use of the mouth and tongue, to stimulate Sex organ. It may be used as foreplay before intercourse, as climax of a sexual act, or even following intercourse. It is sometimes performed to the exclusion of all other forms of sexual activity.
	Oran Oran is a city in northwest Algeria, situated on the Mediterranean Sea coast. During French rule in Algeria Oran was the prefecture of the Oran. It now is the capital of an Oran Province.
	Orange Free State The Orange Free State was an independent country in southern Africa during the second half of the 19th century, and later a Provinces of South Africa in South Africa. It is the historical precursor to the present-day Free State province. Extending between the Orange River and Vaal River rivers, it was established as a free state by Voortrekker settlers, after their departure from the British-dominated Cape Province, and was annexation by the United Kingdom
	Orange juice Orange juice is a fruit juice obtained by squeezing or pressing the interior of an orange . It is enjoyed as a beverage in many parts of the world and is often commonly associated with breakfast. Under U.S. law, products labeled "orange juice" must contain 100 percent real juice and pulp to be labeled as such.
	Orange peel fungus The orange peel fungus is a widespread fungus. It is an extremely distinctive fungus which comprises a wavy-edged, saucer-shaped disc, whose upper surface is bright orange and smooth while the lower surface is greyish orange and rather powdery. The orange peel fungus grows on bare ground, and fruits mainly in the autumn.
	Orange Pekoe Orange Pekoe is a classification of black tea based upon the origin of the leaf. To be classified as pekoe, the tea must be composed purely of the new flushes - a flush being the flower bud plucked with two youngest leaves. The origin of the word pekoe is not definitively known. Suppositions include the Chinese bai hwa "white flower" referring to the flower bud content of pekoe tea, and an Amoy word for the special kind of Chinese tea.
	Orange River The Orange River, in the past also sometimes known as the Gariep or as the Grootrivier, is the major river of South Africa. The river was first discovered by Europeans in 1760 and named after the House of Orange, which was the Stadhouder of Holland between 1777-1779.
	Orangery An Orangery was a feature of royal and aristocratic residences through the 17th and 18th centuries. This type of greenhouse, with citrus trees being grown in tubs and wintering under cover, originated as a part of History of gardens, once glass-making technology enabled sufficient expanses of clear glass to be produced.
	Orangutan The orangutans are two species of Hominidae with long arms and reddish, sometimes brown, hair native to Indonesia and Malaysia . They are the only extant species in the genus Pongo and the subfamily Ponginae, although that subfamily also includes the extinct Gigantopithecus and Sivapithecus genera.
	Orans Orans is a bodily attitude of prayer, usually standing, with the elbows close to the sides of the body and with the hands outstretched sideways, palms up. It is common in Christianity art as early as the wall paintings in the Catacombs of Rome and is still used in both private and communal prayer by both clergy and laity .
	Orca The Orca or Killer Whale is not a whale, but the largest species of the oceanic dolphin family . They are sometimes referred to as blackfish, a group including pilot whales, pygmy killer whale and false killer whales, and melon-headed whales. It is the second-most widely distributed mammal on Earth and is found in all the world's oceans, from the frigid Arctic regions to warm, tropical seas.
	Orchard An orchard is an intentional planting of trees or shrubs maintained for food agriculture. Most orchards comprise either fruit or nut-producing trees, for commercial production. Orchards are also sometimes a feature of large gardens, where they serve an aesthetic as well as a productive purpose.
	Orchard Oriole The Orchard Oriole, Icterus spurius, is a small icterid, 16 cm long and weighing 20 g.. Adults have a pointed bill and white wing bars. The adult male is chestnut on the underparts, shoulder and rump with black everywhere else. The adult female is olive-green on the upper parts, yellowish on the breast and belly.
	Orchestra An orchestra is a musical ensemble used most often in European classical music. A small orchestra is called a chamber orchestra. A full size orchestra may sometimes be called a "symphony orchestra" or "philharmonic orchestra"; these prefixes do not necessarily indicate any strict difference in either the musical instrument constitution or role of the orchestra, but can be useful to distinguish different ensembles based in the same city .
	Orchidaceae Orchids are the largest and most diverse of the flowering plant families, with over 800 described genus and 25,000 species. Some sources give 30,000 species, but the exact number is unknown since classification differs greatly in the academic world. Revisions of different genera occur on a monthly basis and this will increase with the growing use of genetic research and biochemistry.
	Orchidales Orchidales is a botanical name of an Order of flowering plants. In list of systems of plant taxonomy, this is a relatively recent name, as early systems used descriptive botanical names for the order containing the orchids. The Bentham & Hooker system and the Engler systems had the orchids in order Microspermae while the Wettstein system treats them as order Gynandrae.
	Orchis Orchis is a genus in the orchid family. This genus gets its name from the Greek orchis, meaning "testicle", from the appearance of subterranean tuberoids. This genus occurs mainly in Europe, NW Africa, and it stretches as far Tibet, Mongolia, China and Japan. These terrestrial orchids have tubers instead of pseudobulbs.
	Order of Saint Benedict The Order of Saint Benedict — full Latin name: Ordo Sancti Benedicti , initials: OSB — sometimes referred to as the Benedictine Order, is a term used to denote the independent Roman Catholic monasteries that observe the Rule of St Benedict, supplemented by later constitutions and modern customaries.
	Ordinal number Commonly, ordinal numbers, or ordinals for short, are numbers used to denote the position in an Total order sequence: first, second, third, fourth, etc., whereas a cardinal number says "how many there are": one, two, three, four, etc. Here, we describe the mathematics meaning of transfinite ordinal numbers.
	Ordinary An ordinary is an ecclesiastical officer with both pastoral and governmental jurisdiction over a well-defined group of persons granted by canon law in hierarchical Western Christianity. In the Eastern church, such an officer is called a hierarch, which comes from the Greek language word 'ιεραρχης' meaning "high priest."
	Ordnance Ordnance is a general term for a quantity of military equipment, usually specifying the ammunition for artillery, bombs, or other large weapons.
	Ordnance Survey Ordnance Survey is an executive agency of the United Kingdom government. It is the national mapping agency for Great Britain, and one of the world's largest producers of maps.
	Ore An ore is a volume of Rock containing components or minerals in a mode of occurrence which renders it valuable for mining. An ore must contain materials which are: * valuable * in concentrations which can be profitably Mining, transported, milled, and processed. * able to be extracted from waste rock by mineral processing techniques.
	Oregano Oregano or Pot Marjoram is a species of Origanum, native to Europe, the Mediterranean region and southern and central Asia. It is a perennial plant herb, growing to 20-80 cm tall, with opposite leaf 1-4 cm long. The flowers are purple, 3-4 mm long, produced in erect spikes.
	Oregon Oregon is a U.S. state in the Pacific Northwest region of the United States. Oregon borders the Pacific Ocean on the west, Washington on the north, Idaho on the east, and California, and Nevada on the south. Much of its northern border lies along the Columbia River and much of the eastern border lies along the Snake River.
	Oreo Oreo is a trademark for a popular type of sandwich cookie manufactured by the Nabisco Corporation, introduced in 1912. The modern design of the Oreo was developed in 1952 by William A. Turnier. It consists of two circular chocolate wafers, invented by John D. Unger , with a sweet white filling sandwiched between them.
	Orés Or?s is a municipality in the Cinco Villas, in the province of Zaragoza (province), in the autonomous community of Aragon, Spain. It belongs to the comarca of Cinco Villas. It is placed 104 km to the northwest of the provincial capital city, Zaragoza. Its coordinates are: 42? 17' N, 1? 00' W, and is located at 647 m over sea level.
	Organ pipe An organ pipe is one of the tuned resonators that produces the main sound of a pipe organ. Most organ pipes are either long cylindrical metal tubes or elongated wooden boxes of rectangular cross-section. Organ terminology varies a great deal from period to period, style to style and even from builder to builder.
	Organ stop An organ stop can mean one of three things: *The control on an organ console that selects a particular sound. *The mechanism, and in particular the organ pipes, used to produce a particular sound. *The sound itself.
	Organelle In cell biology, an organelle is a discrete structure of a cell having specialized functions. There are many types of organelles, particularly in the eukaryote cells of higher organisms. An organelle is to the cell what an Organ is to the body . Organelles were historically identified through the use of microscopy, and were also identified through the use of cell fractionation.
	Organic chemistry Organic chemistry is a specific discipline within the subject of chemistry. It is the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds of carbon and hydrogen, which may contain any number of other elements, such as nitrogen, oxygen, halogens, and more rarely phosphorus or sulfur .