Building

A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). 　Buildings come in a variety of sizes, shapes, and functions, and have been adapted throughout history for a wide number of factors, from building materials available, to weather conditions, land prices, ground conditions, specific uses, prestige, and aesthetic reasons. 　To better understand the term building compare the list of nonbuilding structures. 　Buildings serve several societal needs – primarily as shelter from weather, security, living space, privacy, to store belongings, and to comfortably live and work. 　A building as a shelter represents a physical division of the human habitat (a place of comfort and safety) and the outside (a place that at times may be harsh and harmful). 　Ever since the first cave paintings, buildings have also become objects or canvasses of much artistic expression. 　In recent years, interest in sustainable planning and building practices has also become an intentional part of the design process of many new buildings and other structures.

Given

Look up given, Given, or ȝiven in Wiktionary, the free dictionary. 　A given is a statement or a condition assumed to be true or known, often to explain or give an example of something; for related topics, see: Presumption (in law) Axiom (in formal logic) Givenness (in discourse) Conditional probability, usually expressed using the term "given" Given may also refer to:

River

A river is a natural flowing watercourse, usually freshwater stream, flowing on the surface or inside caves towards another waterbody at a lower elevation, such as an ocean, sea, bay, lake, wetland or another river. 　In some cases, a river flows into the ground or becomes dry at the end of its course without reaching another body of water. 　Small rivers can be referred to using names such as creek, brook and rivulet. 　There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. 　Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and Northeast England, and "beck" in Northern England. 　Sometimes a river is defined as being larger than a creek, but not always: the language is vague. 　Rivers are an important part of the water cycle. 　Water from a drainage basin generally collects into a river through surface runoff from precipitation, meltwater released from natural ice and snowpacks, and other underground sources such as groundwater recharge and springs. 　Rivers are often considered major features within a landscape; however, they actually only cover around 0.1% of the land on Earth. 　Rivers are also an important natural terraformer, as the erosive action of running water with carve out rills, gullies and valleys in the surface, as well as transferring silt and dissolved minerals downstream, forming river deltas and islands where the flow slows down. 　As a waterbody, rivers also serve crucial ecological functions by providing and feeding habitats for aquatic and semiaquatic animals and plants, especially for migratory fish species. 　Rivers are significant to mankind since many human settlements and civilizations are built around sizeable rivers and streams. 　Most of the major cities of the world are situated on the banks of rivers, as they are (or were) depended upon as a vital source of drinking water, for food supply via fishing and agricultural irrigation, for shipping, as natural borders and/or defensive terrains, as a source of hydropower to drive machinery or generate electricity, for bathing, and as a means of disposing of waste. 　In the pre-industrial era, larger rivers were a major obstacle to movement of people, goods, and armies across regions. 　Towns often developed at the few locations suitable for fording, to build bridges or to support ports, and many major cities such as London are located at the narrowest and most reliable site at which a river could be crossed via bridges or ferries. 　In Earth science disciplines, potamology is the scientific study of rivers, while limnology is the study of inland waters in general.

York

York is a cathedral city in North Yorkshire, England, with Roman origins, sited at the confluence of the rivers Ouse and Foss. 　It is the historic county town of Yorkshire. 　The city has many historic buildings and other structures, such as a minster, castle, and city walls. 　It is the largest settlement and the administrative centre of the wider City of York district. 　The city was founded under the name of Eboracum in 71 AD. 　It then became the capital of the Roman province of Britannia Inferior, and later of the kingdoms of Deira, Northumbria, and Scandinavian York. 　In the Middle Ages, it became the northern England ecclesiastical province's centre, and grew as a wool-trading centre. 　In the 19th century, it became a major railway network hub and confectionery manufacturing centre. 　During the Second World War, part of the Baedeker Blitz bombed the city; it was less affected by the war than other northern cities, with several historic buildings being gutted and restored up to the 1960s. 　The city is one of 15 in England to have a lord mayor, and one of two to have The Right Honourable title affixed, the other being London's. 　Historic governance of the city was as a county corporate, not included in the county's riding system. 　The city has since been covered by a municipal borough, county borough, and since 1996 a non-metropolitan district (the City of York), which also includes surrounding villages and rural areas, and the town of Haxby. 　The current district's local council is responsible for providing all local services and facilities throughout this area. 　The city had a population of 153,717 in the 2011 census; the wider district had a population of 198,100. 　According to 2021[update] census data, the wider district has a population of 202,800, a 2.4% increase compared to the 2011 census.

Room

In a building or large vehicle, like a ship, a room is any enclosed space within a number of walls to which entry is possible only via a door or other dividing structure that connects it to either a passageway, another room, or the outdoors, that is large enough for several people to move about, and whose size, fixtures, furnishings, and sometimes placement within the building or ship support the activity to be conducted in it.

Death

Death is the irreversible cessation of all biological functions that sustain an organism. 　For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain death is sometimes used as a legal definition of death. 　The remains of a former organism normally begin to decompose shortly after death. 　Death is an inevitable process that eventually occurs in almost all organisms. 　Death is generally applied to whole organisms; the similar process seen in individual components of an organism, such as cells or tissues, is necrosis. 　Something that is not considered an organism, such as a virus, can be physically destroyed, but is not said to die. 　As of the early 21st century, over 150,000 humans die each day, with ageing being by far the most common cause of death.　[citation needed] Many cultures and religions have the idea of an afterlife, and also may hold the idea of judgement of good and bad deeds in one's life (heaven, hell, karma).

Data

In the pursuit of knowledge, data (US: /ˈdætə/; UK: /ˈdeɪtə/) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. 　A datum is an individual value in a collection of data. 　Data is usually organized into structures such as tables that provide additional context and meaning, and which may themselves be used as data in larger structures. 　Data may be used as variables in a computational process. 　Data may represent abstract ideas or concrete measurements. 　Data is commonly used in scientific research, economics, and in virtually every other form of human organizational activity. 　Examples of data sets include price indices (such as consumer price index), unemployment rates, literacy rates, and census data. 　In this context, data represents the raw facts and figures which can be used in such a manner in order to capture the useful information out of it. 　Data is collected using techniques such as measurement, observation, query, or analysis, and typically represented as numbers or characters which may be further processed. 　Field data are data that is collected in an uncontrolled in-situ environment. 　Experimental data is data that is generated in the course of a controlled scientific experiment. 　Data is analyzed using techniques such as calculation, reasoning, discussion, presentation, visualization, or other forms of post-analysis. 　Prior to analysis, raw data (or unprocessed data) is typically cleaned: Outliers are removed and obvious instrument or data entry errors are corrected. 　Data can be seen as the smallest units of factual information that can be used as a basis for calculation, reasoning, or discussion. 　Data can range from abstract ideas to concrete measurements, including but not limited to, statistics. 　Thematically connected data presented in some relevant context can be viewed as information. 　Contextually connected pieces of information can then be described as data insights or intelligence. 　The stock of insights and intelligence that accumulates over time resulting from the synthesis of data into information, can then be described as knowledge. 　Data has been described as "the new oil of the digital economy". 　Data, as a general concept, refers to the fact that some existing information or knowledge is represented or coded in some form suitable for better usage or processing. 　Advances in computing technologies have led to the advent of big data, which usually refers to very large quantities of data, usually at the petabyte scale. 　Using traditional data analysis methods and computing, working with such large (and growing) datasets is difficult, even impossible. 　(Theoretically speaking, infinite data would yield infinite information, which would render extracting insights or intelligence impossible.) 　In response, the relatively new field of data science uses machine learning (and other artificial intelligence (AI)) methods that allow for efficient applications of analytic methods to big data.

Form

Look up Form, form, or -form in Wiktionary, the free dictionary. 　Form is the shape, visual appearance, or configuration of an object. 　In a wider sense, the form is the way something happens. 　Form may also refer to: Form (document), a document (printed or electronic) with spaces in which to write or enter data Form (education), a class, set, or group of students Form (religion), an academic term for prescriptions or norms on religious practice Form, a shallow depression or flattened nest of grass used by a hare Form, or rap sheet, slang for a criminal record

Form (zoology)

In zoology, the word "form" or forma (literally Latin for form) is a strictly informal term that is sometimes used to describe organisms. 　Under the International Code of Zoological Nomenclature the term has no standing (it is not accepted). 　In other words, although form names are Latin, and are sometimes wrongly appended to a binomial name, in a zoological context, forms have no taxonomic significance at all.　[citation needed]

Named

Look up named in Wiktionary, the free dictionary. 　Named may refer to something that has been given a name. 　Named may also refer to: named (computing), a widely used DNS server Naming (parliamentary procedure) The Named (band), an American industrial metal group In literature: The Named, a fantasy novel by Marianne Curley The Named, a fictional race of prehistoric big cats, depicted in The Books of the Named series by Clare Bell

Court

A court is any person or institution, often as a government institution, with the authority to adjudicate legal disputes between parties and carry out the administration of justice in civil, criminal, and administrative matters in accordance with the rule of law. 　In both common law and civil law legal systems, courts are the central means for dispute resolution, and it is generally understood that all people have an ability to bring their claims before a court. 　Similarly, the rights of those accused of a crime include the right to present a defense before a court. 　The system of courts that interprets and applies the law is collectively known as the judiciary. 　The place where a court sits is known as a venue. 　The room where court proceedings occur is known as a courtroom, and the building as a courthouse; court facilities range from simple and very small facilities in rural communities to large complex facilities in urban communities. 　The practical authority given to the court is known as its jurisdiction (from Latin iūrisdictiō, from iūris, "of the law," + dīcō, "to declare," + -tiō, noun-forming suffix), the court's power to decide certain kinds of questions or petitions put to it. 　According to William Blackstone's Commentaries on the Laws of England, a court (for civil wrongs) is constituted by a minimum of three parties: the āctor or plaintiff, who complains of an injury done; the reus or defendant, who is called upon to make satisfaction for it; and the jūdex or judicial power, who is to examine the truth of the fact, determine the law arising upon that fact, and, if any injury appears to have been done, ascertain and by its officers apply a legal remedy. 　It is also usual in the superior courts to have barristers, and attorneys or counsel, as assistants, though, often, courts consist of additional barristers, bailiffs, reporters, and perhaps a jury. 　The term "the court" is also used to refer to the presiding officer or officials, usually one or more judges. 　The judge or panel of judges may also be collectively referred to as "the bench" (in contrast to attorneys and barristers, collectively referred to as "the bar"). 　In the United States, the legal authority of a court to take action is based on personal jurisdiction over the parties to the litigation and subject-matter jurisdiction over the claims asserted.

King

King is the title given to a male monarch in a variety of contexts. 　The female equivalent is queen, which title is also given to the consort of a king, although in some cases, the title of King is given to females such as in the case of Mary, Queen of Hungary. 　In the context of prehistory, antiquity and contemporary indigenous peoples, the title may refer to tribal kingship. 　Germanic kingship is cognate with Indo-European traditions of tribal rulership (c.f. Indic rājan, Gothic reiks, and Old Irish rí, etc.). 　In the context of classical antiquity, king may translate in Latin as rex and in Greek as archon or basileus. 　In classical European feudalism, the title of king as the ruler of a kingdom is understood to be the highest rank in the feudal order, potentially subject, at least nominally, only to an emperor (harking back to the client kings of the Roman Republic and Roman Empire). 　In a modern context, the title may refer to the ruler of one of a number of modern monarchies (either absolute or constitutional). 　The title of king is used alongside other titles for monarchs: in the West, emperor, grand prince, prince, archduke, duke or grand duke, and in the Islamic world, malik, sultan, emir or hakim, etc. 　The city-states of the Aztec Empire had a Tlatoani, which were kings of pre-Hispanic Mesoamerica. 　The Huey Tlatoani was the emperor of the Aztecs. 　The term king may also refer to a king consort, a title that is sometimes given to the husband of a ruling queen, but the title of prince consort is more common.

History

History (derived from Ancient Greek ἱστορία (historía) 'inquiry; knowledge acquired by investigation') is the systematic study and documentation of human activity. 　The time period of events before the invention of writing systems is considered prehistory. 　"History" is an umbrella term comprising past events as well as the memory, discovery, collection, organization, presentation, and interpretation of these events. 　Historians seek knowledge of the past using historical sources such as written documents, oral accounts, art and material artifacts, and ecological markers. 　History is not complete and still has debatable mysteries. 　History is also an academic discipline which uses narrative to describe, examine, question, and analyze past events, and investigate their patterns of cause and effect. 　Historians often debate which narrative best explains an event, as well as the significance of different causes and effects. 　Historians also debate the nature of history as an end in itself, as well as its usefulness to give perspective on the problems of the present. 　Stories common to a particular culture, but not supported by external sources (such as the tales surrounding King Arthur), are usually classified as cultural heritage or legends. 　History differs from myth in that it is supported by verifiable evidence. 　However, ancient cultural influences have helped spawn variant interpretations of the nature of history which have evolved over the centuries and continue to change today. 　The modern study of history is wide-ranging, and includes the study of specific regions and the study of certain topical or thematic elements of historical investigation. 　History is often taught as a part of primary and secondary education, and the academic study of history is a major discipline in university studies. 　Herodotus, a 5th-century BC Greek historian, is often considered the "father of history" (as he was one of the first historians) in the Western tradition, although he has also been criticized as the "father of lies". 　Along with his contemporary Thucydides, he helped form the foundations for the modern study of past events and societies. 　Their works continue to be read today, and the gap between the culture-focused Herodotus and the military-focused Thucydides remains a point of contention or approach in modern historical writing. 　In East Asia, a state chronicle, the Spring and Autumn Annals, was reputed to date from as early as 722 BC, although only 2nd-century BC texts have survived.

March

March is the third month of the year in both the Julian and Gregorian calendars. 　It is the second of seven months to have a length of 31 days. 　In the Northern Hemisphere, the meteorological beginning of spring occurs on the first day of March. 　The March equinox on the 20 or 21 marks the astronomical beginning of spring in the Northern Hemisphere and the beginning of autumn in the Southern Hemisphere, where September is the seasonal equivalent of the Northern Hemisphere's March.

White

White is the lightest color and is achromatic (having no hue). 　It is the color of objects such as snow, chalk, and milk, and is the opposite of black. 　White objects fully reflect and scatter all the visible wavelengths of light. 　White on television and computer screens is created by a mixture of red, blue, and green light. 　The color white can be given with white pigments, especially titanium dioxide. 　In ancient Egypt and ancient Rome, priestesses wore white as a symbol of purity, and Romans wore white togas as symbols of citizenship. 　In the Middle Ages and Renaissance a white unicorn symbolized chastity, and a white lamb sacrifice and purity. 　It was the royal color of the kings of France, and of the monarchist movement that opposed the Bolsheviks during the Russian Civil War (1917–1922). 　Greek temples and Roman temples were faced with white marble, and beginning in the 18th century, with the advent of neoclassical architecture, white became the most common color of new churches, capitols and other government buildings, especially in the United States. 　It was also widely used in 20th century modern architecture as a symbol of modernity and simplicity. 　According to surveys in Europe and the United States, white is the color most often associated with perfection, the good, honesty, cleanliness, the beginning, the new, neutrality, and exactitude. 　White is an important color for almost all world religions. 　The pope, the head of the Roman Catholic Church, has worn white since 1566, as a symbol of purity and sacrifice. 　In Islam, and in the Shinto religion of Japan, it is worn by pilgrims. 　In Western cultures and in Japan, white is the most common color for wedding dresses, symbolizing purity and virginity. 　In many Asian cultures, white is also the color of mourning.

September

September is the ninth month of the year in both the Julian and Gregorian calendars, the third of four months to have a length of 30 days, and the fourth of five months to have a length of fewer than 31 days. 　September in the Northern Hemisphere and March in the Southern Hemisphere are seasonally equivalent. 　In the Northern hemisphere, the beginning of the meteorological autumn is on 1 September. 　In the Southern hemisphere, the beginning of the meteorological spring is on 1 September.　 　September marks the beginning of the ecclesiastical year in the Eastern Orthodox Church. 　It is the start of the academic year in many countries of the northern hemisphere, in which children go back to school after the summer break, sometimes on the first day of the month. 　September (from Latin septem, "seven") was originally the seventh of ten months in the oldest known Roman calendar, the calendar of Romulus c. 　750 BC, with March (Latin Martius) the first month of the year until perhaps as late as 451 BC. 　After the calendar reform that added January and February to the beginning of the year, September became the ninth month but retained its name. 　It had 29 days until the Julian reform, which added a day.

Book

A book is a medium for recording information in the form of writing or images, typically composed of many pages (made of papyrus, parchment, vellum, or paper) bound together and protected by a cover. 　The technical term for this physical arrangement is codex (plural, codices). 　In the history of hand-held physical supports for extended written compositions or records, the codex replaces its predecessor, the scroll. 　A single sheet in a codex is a leaf and each side of a leaf is a page. 　As an intellectual object, a book is prototypically a composition of such great length that it takes a considerable investment of time to compose and still considered as an investment of time to read. 　In a restricted sense, a book is a self-sufficient section or part of a longer composition, a usage reflecting that, in antiquity, long works had to be written on several scrolls and each scroll had to be identified by the book it contained. 　Each part of Aristotle's Physics is called a book. 　In an unrestricted sense, a book is the compositional whole of which such sections, whether called books or chapters or parts, are parts. 　The intellectual content in a physical book need not be a composition, nor even be called a book. 　Books can consist only of drawings, engravings or photographs, crossword puzzles or cut-out dolls. 　In a physical book, the pages can be left blank or can feature an abstract set of lines to support entries, such as in an account book, an appointment book, an autograph book, a notebook, a diary or a sketchbook. 　Some physical books are made with pages thick and sturdy enough to support other physical objects, like a scrapbook or photograph album. 　Books may be distributed in electronic form as ebooks and other formats. 　Although in ordinary academic parlance a monograph is understood to be a specialist academic work, rather than a reference work on a scholarly subject, in library and information science monograph denotes more broadly any non-serial publication complete in one volume (book) or a finite number of volumes (even a novel like Proust's seven-volume In Search of Lost Time), in contrast to serial publications like a magazine, journal or newspaper. 　An avid reader or collector of books is a bibliophile or colloquially, "bookworm". 　A place where books are traded is a bookshop or bookstore. 　Books are also sold elsewhere and can be borrowed from libraries. 　Google has estimated that by 2010, approximately 130,000,000 titles had been published. 　In some wealthier nations, the sale of printed books has decreased because of the increased usage of ebooks. 　Although in most countries printed books continue to outsell their digital counterparts due to many people still preferring to read in a traditional way.

Night

Night (also described as nighttime, unconventionally spelled as "nite") is the period of ambient darkness from sunset to sunrise during each 24-hour day, when the Sun is below the horizon. 　The exact time when night begins and ends depends on the location and varies throughout the year, based on factors such as season and latitude. 　The word can be used in a different sense as the time between bedtime and morning. 　In common communication, it is a farewell (sometimes lengthened to "good night"), mainly when someone is going to sleep or leaving. 　Astronomical night is the period between astronomical dusk and astronomical dawn when the Sun is between 18 and 90 degrees below the horizon and does not illuminate the sky. 　As seen from latitudes between about 48.56° and 65.73° north or south of the equator, complete darkness does not occur around the summer solstice because, although the Sun sets, it is never more than 18° below the horizon at lower culmination, −90° Sun angles occur at the Tropic of Cancer on the December solstice and Tropic of Capricorn on the June solstice, and at the equator on equinoxes. 　And as seen from latitudes greater than 72° north or south of the equator, complete darkness does not occur in both equinoxes because, although the Sun sets, it is never more than 18° below the horizon. 　The opposite of night is day (or "daytime", to distinguish it from "day" referring to a 24-hour period). 　Twilight is the period of night after sunset or before sunrise when the Sun still illuminates the sky when it is below the horizon. 　At any given time, one side of Earth is bathed in sunlight (the daytime), while the other side is in darkness caused by Earth blocking the sunlight. 　The central part of the shadow is called the umbra, where the night is darkest. 　Natural illumination at night is still provided by a combination of moonlight, planetary light, starlight, zodiacal light, gegenschein, and airglow. 　In some circumstances, aurorae, lightning, and bioluminescence can provide some illumination. 　The glow provided by artificial lighting is sometimes referred to as light pollution because it can interfere with observational astronomy and ecosystems.

Must

Must (from the Latin vinum mustum, "young wine") is freshly crushed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. 　The solid portion of the must is called pomace and typically makes up 7–23% of the total weight of the must. 　Making must is the first step in winemaking. 　Because of its high glucose content, typically between 10 and 15%, must is also used as a sweetener in a variety of cuisines. 　Unlike commercially sold grape juice, which is filtered and pasteurized, must is thick with particulate matter, opaque, and comes in various shades of brown and purple.

Present

The present (or here and now) is the time that is associated with the events perceived directly and in the first time, not as a recollection (perceived more than once) or a speculation (predicted, hypothesis, uncertain). 　It is a period of time between the past and the future, and can vary in meaning from being an instant to a day or longer. 　It is sometimes represented as a hyperplane in space-time, typically called "now", although modern physics demonstrates that such a hyperplane cannot be defined uniquely for observers in relative motion. 　The present may also be viewed as a duration (see specious present).

Species

In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. 　A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. 　Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. 　In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. 　The most recent rigorous estimate for the total number of species of eukaryotes is between 8 and 8.7 million. 　However, only about 14% of these had been described by 2011. 　All species (except viruses) are given a two-part name, a "binomial". 　The first part of a binomial is the genus to which the species belongs. 　The second part is called the specific name or the specific epithet (in botanical nomenclature, also sometimes in zoological nomenclature). 　For example, Boa constrictor is one of the species of the genus Boa, with constrictor being the species' epithet. 　While the definitions given above may seem adequate at first glance, when looked at more closely they represent problematic species concepts. 　For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. 　Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies. 　Although none of these are entirely satisfactory definitions, and while the concept of species may not be a perfect model of life, it is still an incredibly useful tool to scientists and conservationists for studying life on Earth, regardless of the theoretical difficulties. 　If species were fixed and clearly distinct from one another, there would be no problem, but evolutionary processes cause species to change. 　This obliges taxonomists to decide, for example, when enough change has occurred to declare that a lineage should be divided into multiple chronospecies, or when populations have diverged to have enough distinct character states to be described as cladistic species. 　Species were seen from the time of Aristotle until the 18th century as fixed categories that could be arranged in a hierarchy, the great chain of being. 　In the 19th century, biologists grasped that species could evolve given sufficient time. 　Charles Darwin's 1859 book On the Origin of Species explained how species could arise by natural selection. 　That understanding was greatly extended in the 20th century through genetics and population ecology. 　Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures. 　Genes can sometimes be exchanged between species by horizontal gene transfer; new species can arise rapidly through hybridisation and polyploidy; and species may become extinct for a variety of reasons. 　Viruses are a special case, driven by a balance of mutation and selection, and can be treated as quasispecies.

Light

Light or visible light is electromagnetic radiation that can be perceived by the human eye. 　Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahertz, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths). 　In physics, the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not. 　In this sense, gamma rays, X-rays, microwaves and radio waves are also light. 　The primary properties of light are intensity, propagation direction, frequency or wavelength spectrum and polarization. 　Its speed in vacuum, 299792458 m/s, is one of the fundamental constants of nature. 　Like all types of electromagnetic radiation, visible light propagates by massless elementary particles called photons that represents the quanta of electromagnetic field, and can be analyzed as both waves and particles. 　The study of light, known as optics, is an important research area in modern physics. 　The main source of natural light on Earth is the Sun. 　Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. 　With the development of electric lights and power systems, electric lighting has effectively replaced firelight.

Need

A need is dissatisfaction at a point of time and in a given context. 　Needs are distinguished from wants. 　In the case of a need, a deficiency causes a clear adverse outcome: a dysfunction or death. 　In other words, a need is something required for a safe, stable and healthy life (e.g. air, water, food, land, shelter) while a want is a desire, wish or aspiration. 　When needs or wants are backed by purchasing power, they have the potential to become economic demands. 　Basic needs such as air, water, food and protection from environmental dangers are necessary for an organism to live. 　In addition to basic needs, humans also have needs of a social or societal nature such as the human need to socialise or belong to a family unit or group. 　Needs can be objective and physical, such as the need for food, or psychical and subjective, such as the need for self-esteem. 　The concept of "unmet need" arises in relation to needs in a social context which are not being fulfilled. 　Needs and wants are a matter of interest in, and form a common substrate for, the fields of philosophy, biology, psychology, social science, economics, marketing and politics.

Art

Art is a diverse range of human activity, and resulting product, that involves creative or imaginative talent expressive of technical proficiency, beauty, emotional power, or conceptual ideas. 　There is no generally agreed definition of what constitutes art, and its interpretation has varied greatly throughout history and across cultures. 　In the Western tradition, the three classical branches of visual art are painting, sculpture, and architecture. 　Theatre, dance, and other performing arts, as well as literature, music, film and other media such as interactive media, are included in a broader definition of the arts. 　Until the 17th century, art referred to any skill or mastery and was not differentiated from crafts or sciences. 　In modern usage after the 17th century, where aesthetic considerations are paramount, the fine arts are separated and distinguished from acquired skills in general, such as the decorative or applied arts. 　The nature of art and related concepts, such as creativity and interpretation, are explored in a branch of philosophy known as aesthetics. 　The resulting artworks are studied in the professional fields of art criticism and the history of art.