SI is the International System of Units. SI, Si, or si may also refer to:

Arts, entertainment, and media

Literature

* ''Si'' (novel), a 2014 novel by Bob Ong * ''Sí'' (Peruvian magazine), a magazine notable for its anti-corruption reporting * ''

Skeptical Inquirer ''Skeptical Inquirer'' (S.I.) is a bimonthly American general-audience magazine published by the Committee for Skeptical Inquiry (CSI) with the subtitle "The Magazine for Science and Reason". The magazine initially focused on investigating clai ...

'', an American magazine covering topics on science and skepticism * ''

Sports Illustrated ''Sports Illustrated'' (''SI'') is an American sports magazine first published in August 1954. Founded by Stuart Scheftel, it was the first magazine with a circulation of over one million to win the National Magazine Award for General Excellen ...

'', an American sports magazine

Music

* ''Sí'' (Julieta Venegas album), released in 2003 * ''Sì'' (Andrea Bocelli album), released in 2018 * "Sí" (Martin Jensen song), a 2015 song * Si (musical note), the seventh note in the traditional fixed do solfège * ''Sì'' (operetta), an operetta by the Italian composer Pietro Mascagni * "Sì" (Gigliola Cinquetti song), the Italian entry to the Eurovision Song Contest 1974 *

Si (Zaz song) "Si" is a song by French singer-songwriter Zaz, released as a single from the 2013 album Recto Verso. Chart positions References 2013 songs {{2010s-song-stub ...

, 2013 * ''Sí'', a 2013 Spanish album by

Malú María Lucía Sánchez Benítez, known as Malú, is a Spanish singer. She is the niece of the composer and guitarist Paco de Lucía, and is known for songs such as "Aprendiz", "Como Una Flor", "Toda", "Diles", "Si Estoy Loca" and "No Voy a Cambi ...

* "Sì", a 1985 song released by Italian actress

Carmen Russo ''Carmen'' () is an opera in four acts by the French composer Georges Bizet. The libretto was written by Henri Meilhac and Ludovic Halévy, based on the novella of the same title by Prosper Mérimée. The opera was first performed by the Op ...

Other uses in arts, entertainment, and media

* ''Si'' (film), original title of the 2010 South Korean film ''Poetry''

Enterprises and organisations

Computing

* Swiss Informatics Society, a Swiss organization of computer science educators, researchers, and professionals *

The SI Vencore, Inc. was a private defense contractor that serves the U.S. Intelligence Community, Department of Defense and other agencies. From 2010 to 2014, the company was named The SI Organization, Inc. (the SI). The SI provided full life cycle, m ...

, a former name of the American defense contractor Vencore

Education

St. Ignatius College Preparatory St. Ignatius College Preparatory, colloquially referred to by Bay Area locals as SI, is a private, Catholic preparatory school in the Jesuit tradition, serving the San Francisco Bay Area since 1855. Located in the Archdiocese of San Francisco, ...

, a Jesuit high school in San Francisco, California, US * Silay Institute, a private college in the Philippines

Government

* Si, a South Korean administrative unit *

Survey of India The Survey of India is India's central engineering agency in charge of mapping and surveying.Swedish Institute The Swedish Institute (, ) is a government agency in Sweden with the responsibility to spread information about Sweden outside the country. It exists to promote Swedish interests, and to organise exchanges with other countries in different ar ...

(''Svenska institutet''), a Swedish government agency which promotes Sweden abroad

Politics

Sarekat Islam Sarekat Islam or Syarikat Islam ( 'Islamic Association' or 'Islamic Union'; SI) was an Indonesian socio-political organization founded at the beginning of the 20th century during the Dutch colonial era. Initially, SI served as a cooperative of ...

, a socio-political organization in Indonesia under Dutch colonial rule *

Catalan Solidarity for Independence Catalan Solidarity for Independence ( Catalan: ''Solidaritat Catalana per la Independència'', ''SI''; ) is an electoral coalition in Catalonia, founded in the summer of 2010 as an outcome of the grassroots social movement that initiated and orga ...

, a Catalan political party *

Situationist International The Situationist International (SI) was an international organization of social revolutionaries made up of avant-garde artists, intellectuals, and political theorists. It was prominent in Europe from its formation in 1957 to its dissolution ...

, an organization of social revolutionaries *

Socialist International The Socialist International (SI) is a political international or worldwide organisation of political parties which seek to establish democratic socialism, consisting mostly of Social democracy, social democratic political parties and Labour mov ...

, a worldwide organization of political parties *

Solidarity and Equality Solidarity and Equality (, or simply SI) is a centre-left Argentine political party, founded in 2008 as a splinter from ARI. As part of building a broader coalition ahead of the 2007 elections, the ARI leader Elisa Carrió reached out to centris ...

, an Argentine political party (Spanish: ''Solidaridad e Igualdad'')

Transportation

Blue Islands Blue Islands Limited is a regional airline of the Channel Islands. Its head office is in Forest, Guernsey, and its registered office is in Saint Anne, Alderney. It operates scheduled services from and within the Channel Islands to the United ...

(IATA airline code, SI) *

Skynet Airlines Skynet Airlines was an airline operating from Ireland to Russia via Amsterdam, that was operational between 2001 and 2004.Spokane International Railroad The Spokane International Railroad was a short line railroad between Spokane, Washington, and the Canadian Pacific Railway (CP) at Kingsgate, British Columbia. The line became an important one for the CP with its connections to the Union Paci ...

(reporting mark SI), a former railway in Washington, US

Other enterprises and organizations

Samahang Ilokano The Confederation of Ilocano Association, Inc., doing business as Samahang Ilokano (lit., Ilocano Association), is an International fraternity and sorority composed of students and graduates from colleges and universities in the northern part ...

, a fraternity/sorority based in the Philippines * SÍ Sørvágur, a Faroese sports association *

Society of Indexers The Society of Indexers (SI) is a professional society of indexers based in the UK, with its offices in Sheffield, England, but has members worldwide. The society was established in 1957, while its quarterly journal, ''The Indexer'' has been pub ...

, a professional society based in the UK *

Sports Interactive Sports Interactive Limited is a British video game developer based in London, best known for the ''Football Manager'' series. Founded by brothers Collyer brothers (game designers), Oliver and Paul Collyer in July 1994, the studio was acquired in ...

, a British computer games development company

People with the name

Si (surname) Si is the pinyin romanization of a number of distinct Chinese surnames that are written with different characters in Chinese. Depending on the character, it may be spelled Sī, Sí, Sǐ, or Sì when tone diacritics are used. In Wade–Giles they ...

, a Chinese surname *

Si (given name) Si is a given name, which is often a nickname or a short version of Simon, Silas, or other names. It may refer to the following notable people: *Si Begg (born 1972), English electronic dance music DJ, musician and record producer *Si Bell (1894–19 ...

Princess Si of Anding Princess Si of Anding (安定思公主, 19th March(?) 654 – 654) was a princess of Chinese Tang dynasty, who was posthumously honored with the title Princess Anding, along with the posthumous name Si in 664. Princess Si was the first daughter ...

,first daughter of Wu zetain

Places

Mount Si Mount Si (pronounced ; , ) is a mountain in the northwest United States, east of Seattle, Washington. It lies on the western margin of the Cascade Range just above the coastal plains around Puget Sound, and towers over the nearby town of North B ...

, a mountain in the U.S. state of Washington *

Province of Siena The province of Siena (, ) is a Provinces of Italy, province in the Tuscany region of Italy. Its capital is the city of Siena. It has 259,826 inhabitants. Geography The province is divided into seven historical areas: * Alta Val d'Elsa * Chian ...

(postal code and vehicle registration plate code) *

Si County Si County or Sixian is a county in northeast Anhui Province, China. It borders the northern part of Jiangsu Province to the north and east and is under the administration of the prefecture-level city of Suzhou. Name Si County is named for the Si ...

, Anhui, China *

Si River The Si River (Chinese: 泗河, pinyin: Sì Hé; formerly 泗水, pinyin: Sì Shuǐ) is a river in Shandong Province, eastern China. It also ran through the area of modern Jiangsu Province until floods changed its course in 1194. Course The S ...

, in China *

Slovenia Slovenia, officially the Republic of Slovenia, is a country in Central Europe. It borders Italy to the west, Austria to the north, Hungary to the northeast, Croatia to the south and southeast, and a short (46.6 km) coastline within the Adriati ...

's ISO 3166-2 code

Science and technology

Biology and healthcare

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums, Education center, education and Research institute, research centers, created by the Federal government of the United States, U.S. government "for the increase a ...

(SI is its international code) *

Sacroiliac The sacroiliac joint or SI joint (SIJ) is the joint between the sacrum and the ilium bones of the pelvis, which are connected by strong ligaments. In humans, the sacrum supports the spine and is supported in turn by an ilium on each side. The j ...

, an anatomical abbreviation for the sacroiliac (joint) *

Self-injury Self-harm refers to intentional behaviors that cause harm to oneself. This is most commonly regarded as direct injury of one's own skin tissues, usually without suicidal intention. Other terms such as cutting, self-abuse, self-injury, and s ...

, intentional, direct injuring * Shock index, a measurement used to determine if a person is suffering shock

Chemistry

* si, a chemical descriptor; See

prochirality In stereochemistry, prochiral molecules are those that can be converted from achiral to Chirality (chemistry), chiral in a single Reaction step, step, such as changing one atom. An achiral species which can be converted to a chiral in two steps i ...

Silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

, symbol Si, a chemical element *

Disulfur diiodide Disulfur diiodide is an unstable inorganic chemical compound with the chemical formula . It is a red-brown solid that decomposes above −30 °C to elemental sulfur and iodine. Production Reaction of sulfur and iodine The first attempt and claim ...

, empirical formula SI

Computing and Internet

* .si, the Internet country code top-level domain for Slovenia *

Shift In Shift Out (SO) and Shift In (SI) are ASCII control characters 14 and 15, respectively (0x0E and 0x0F). These are sometimes also called "Control-N" and "Control-O". The original purpose of these characters was to provide a way to shift a coloured ...

, an ASCII control character *

SI register x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. The ...

, or source index, in X86 computer architecture *

Swarm intelligence Swarm intelligence (SI) is the collective behavior of decentralized, self-organized systems, natural or artificial. The concept is employed in work on artificial intelligence. The expression was introduced by Gerardo Beni and Jing Wang in 198 ...

, an artificial intelligence technique *

Synthetic intelligence Synthetic intelligence (SI) is an alternative/opposite term for artificial intelligence emphasizing that the intelligence of machines need not be an imitation or in any way artificial; it can be a genuine form of intelligence. John Haugeland prop ...

, an alternate term for or a form of artificial intelligence

Medical

Suicidal ideation Suicidal ideation, or suicidal thoughts, is the thought process of having ideas or ruminations about the possibility of dying by suicide.World Health Organization, ''ICD-11 for Mortality and Morbidity Statistics'', ver. 09/2020MB26.A Suicidal i ...

, thoughts of suicide *

, nonsuicidal injuring of the body

Motor vehicles

Honda Civic Si commonly known as just Honda, is a Japanese multinational conglomerate automotive manufacturer headquartered in Minato, Tokyo, Japan. Founded in October 1946 by Soichiro Honda, Honda has been the world's largest motorcycle manufacturer sin ...

, an automobile *

Spark-ignition engine A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to compression-ignition engines, ty ...

, a type of internal combustion engine

Other uses in science and technology

Signal integrity Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage (or current) waveform. However, digital signals are fundamentally analog signal, anal ...

, electronic circuit tools and techniques that ensure electrical signals are of sufficient quality *

Sine integral In mathematics, trigonometric integrals are a indexed family, family of nonelementary integrals involving trigonometric functions. Sine integral The different sine integral definitions are \operatorname(x) = \int_0^x\frac\,dt \operato ...

, Si(x) *

Spectral interferometry Spectral interferometry (SI) or frequency-domain interferometry is a linear technique used to measure optical pulses, with the condition that a reference pulse that was previously characterized is available. This technique provides information abou ...

, attosecond physics technique

Titles and ranks

* Si, a Maghrebi Arabic variant of

Sidi ''Sidi'' or ''Sayidi'', also Sayyidi and Sayeedi, ( (dialectal) "milord") is an Arabic masculine title of respect. ''Sidi'' is used often to mean "saint" or "my master" in Maghrebi Arabic and Egyptian Arabic. Without the first person possessiv ...

, a title of respect * Si, a variant of the Thai honorific Sri *

Station inspector Station inspector is a police rank used in some countries. Singapore Singapore Police Force Station inspector is the highest non-commissioned officer, non-commissioned rank in the Singapore Police Force, below inspector, and above senior staff ...

, a rank in the Singapore Police Force *

Sub-inspector Sub-inspector (SI), or sub-inspector of police or police sub-inspector (PSI), is a rank used extensively in South Asia: in the police forces of Bangladesh, Pakistan, India, and Sri Lanka, which are primarily based on the British model. It was form ...

, a rank in Indian Police forces

Other uses

Statutory instrument (UK) A statutory instrument (SI) is the principal form in which delegated legislation is made in Great Britain. Statutory instruments are governed by the Statutory Instruments Act 1946.Sì (dessert) Sì (pronounced , , transcribed as sì in Foochow Romanized) is a traditional spherical dessert made from glutinous rice, eaten in celebration of the Winter Solstice festival in Fuzhou, Fujian Province, China. It is usually produced without fill ...

, a Chinese dessert * , , or , Celtic mythological beings * si, the

Sinhala language Sinhala ( ; Sinhala: , , ), sometimes called Sinhalese ( ), is an Indo-Aryan language primarily spoken by the Sinhalese people of Sri Lanka, who make up the largest ethnic group on the island, numbering about 16 million. It is also the first ...

ISO 639 alpha-2 code *

Supplemental instruction Supplemental instruction (SI) is an academic support model that uses peer learning to improve university student retention and student success in high-attrition courses.Blanc, Robert A., Larry E. DeBuhr, and Deanna C. Martin. “Breaking the Attrit ...

, an academic support program often used in higher education