Si

SI is the International System of Units.

SI, Si, or si may also refer to:

Literature

 * Si (novel), a 2014 novel by Bob Ong
 * Sí (Peruvian magazine), a magazine notable for its anti-corruption reporting
 * Skeptical Inquirer, an American magazine covering topics on science and skepticism
 * Sports Illustrated, 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), 2013
 * Sí, a 2013 Spanish album by Malú
 * "Sì", a 1985 song released by Italian actress Carmen Russo

Other uses in arts, entertainment, and media

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

Computing

 * Swiss Informatics Society, a Swiss organization of computer science educators, researchers, and professionals
 * The SI, a former name of the American defense contractor Vencore

Education

 * St. Ignatius College Preparatory, 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, an Indian government agency responsible for managing geographical information
 * Swedish Institute (Svenska institutet), a Swedish government agency which promotes Sweden abroad

Politics

 * Sarekat Islam, a socio-political organization in Indonesia under Dutch colonial rule
 * Catalan Solidarity for Independence, a Catalan political party
 * Situationist International, an organization of social revolutionaries
 * Socialist International, a worldwide organization of political parties
 * Solidarity and Equality, an Argentine political party (Spanish: Solidaridad e Igualdad)

Transportation

 * Blue Islands (IATA airline code, SI)
 * Skynet Airlines (IATA airline code SI, ceased operating 2004)
 * Spokane International Railroad (reporting mark SI), a former railway in Washington, US

Other enterprises and organizations

 * Samahang Ilokano, a fraternity/sorority based in the Philippines
 * SÍ Sørvágur, a Faroese sports association
 * Society of Indexers, a professional society based in the UK
 * Sports Interactive, a British computer games development company

People with the name

 * Si (surname), a Chinese surname
 * Si (given name)

Places

 * Mount Si, a mountain in the U.S. state of Washington
 * Province of Siena (postal code and vehicle registration plate code)
 * Si County, Anhui, China
 * Si River, in China
 * Slovenia's ISO 3166-2 code

Biology and healthcare

 * Sacroiliac, an anatomical abbreviation for the sacroiliac (joint)
 * Self-injury, intentional, direct injuring
 * Shock index, a measurement used to determine if a person is suffering shock

Chemistry

 * si, a chemical descriptor; See prochirality
 * Silicon, symbol Si, a chemical element
 * Disulfur diiodide, empirical formula SI

Computing and Internet

 * .si, the Internet country code top-level domain for Slovenia
 * Shift In, an ASCII control character
 * SI register, or source index, in X86 computer architecture
 * Swarm intelligence, an artificial intelligence technique
 * Synthetic intelligence, an alternate term for or a form of artificial intelligence

Motor vehicles

 * Honda Civic Si, an automobile
 * Spark-ignition engine, a type of internal combustion engine

Other uses in science and technology

 * Signal integrity, electronic circuit tools and techniques that ensure electrical signals are of sufficient quality
 * Sine integral, Si(x)
 * Spectral interferometry, attosecond physics technique

Titles and ranks

 * Si, a Maghrebi Arabic variant of Sidi, a title of respect
 * Si, a variant of the Thai honorific Sri
 * Station inspector, a rank in the Singapore Police Force
 * Sub-inspector, a rank in Indian Police forces

Other uses

 * Statutory instrument (UK), abbreviated SI, the principal form in which delegated legislation is made in Great Britain
 * Sì (dessert), a Chinese dessert
 * Sídhe, Sí, or Sìth, Celtic mythological beings
 * si, the Sinhala language ISO 639 alpha-2 code
 * Supplemental instruction, an academic support program often used in higher education