Io most commonly refers to: *

Io (moon) Io () is the innermost and second-smallest of the four Galilean moons of the planet Jupiter. Slightly larger than Earth's Moon, Io is the list of natural satellites, fourth-largest natural satellite in the Solar System, has the highest density ...

, a moon of Jupiter *

Io (mythology) In Greek mythology, Io (; ) was one of the mortal lovers of Zeus. An Argive princess, she was an ancestor of many kings and heroes, such as Perseus, Cadmus, Heracles, Minos, Lynceus, Cepheus, and Danaus. The astronomer Simon Marius named a ...

, daughter of Inachus in Greek mythology, and lover of Zeus who was turned into a cow Io, IO, iO, I/O, i/o, or i.o. may also refer to:

Arts, entertainment and media

Fictional elements

Scylla Io This article comprises a list of characters that play a role in ''Saint Seiya'' (also known as ''Knights of the Zodiac'') and its canonical continuation, ''Saint Seiya: Next Dimension'', two manga series created, written and illustrated by Masami ...

, one of Poseidon's Marine Generals in the ''Saint Seiya'' series *A ''Dungeons & Dragons'' dragon deity *Io Otonashi, a main character in the Japanese manga series ''

Place to Place is a Japanese four-panel manga series written and illustrated by Ishiki. The manga began serialisation in Houbunsha's ''Manga Time Kirara'' magazine in 2006 and the chapters collected into 9 volumes as of 27 September 2022. An anime televi ...

'' (''Acchi Kocchi'') *Io Nitta, a character in the game '' Shin Megami Tensei: Devil Survivor 2''

Gaming

*''iO'', a 2014 video game by Gamious *

IO Interactive IO Interactive A/S (IOI) is a Danish video game developer and publisher based in Copenhagen, best known for creating and developing the ''Hitman'' and '' Kane and Lynch'' franchises. IO Interactive's most recent game is '' Hitman 3'', which was ...

, a Danish computer game developer

Music

* IO (German band), a German band *

Io (English band) io is an English experimental rock band from Birmingham, England. The band currently consists of Al Lawson (guitar/vocals), Stu Atkins (guitar), Dave Wright (drums), and Steve Wood (bass). The band formed in 2006 after the collapse of two Bir ...

, an English band * I_o (musician), an American DJ and record producer (1990–2020) * ''i/o'' (Peter Gabriel album), 2023

Theatre and opera

* ''Io'' (opera), an unfinished ''acte de ballet'' (opera) by Jean-Philippe Rameau *

iO Theater iO, or iO Chicago, (formerly known as ImprovOlympic) is an improv theater and training center in central Chicago. The theater teaches and hosts performances of improvisational comedy. It was founded in 1981 by Del Close and Charna Halpern. The ...

(ImprovOlympic), a theater in Chicago, Illinois, dedicated to improvisational comedy *

IO West iO, or iO Chicago, (formerly known as ImprovOlympic) is an improv theater and training center in central Chicago. The theater teaches and hosts performances of improvisational comedy. It was founded in 1981 by Del Close and Charna Halpern. The ...

, a Los Angeles theater associated with the Chicago iO

Other uses in arts, entertainment and media

* ''EO'' (original Polish title: ''IO''), a 2022 Jerzy Skolimowski film * ''Io'' (film), a 2019 Netflix film * iO Digital Cable Service, a service offered by Cablevision *''

International Organization An international organization, also known as an intergovernmental organization or an international institution, is an organization that is established by a treaty or other type of instrument governed by international law and possesses its own le ...

'', a peer-reviewed journal that covers the entire field of international affairs

Business and economics

Industrial and organizational psychology Industrial and organizational psychology (I-O psychology) "focuses the lens of psychological science on a key aspect of human life, namely, their work lives. In general, the goals of I-O psychology are to better understand and optimize the effec ...

, the field of psychology that studies work, academic, and other organizational issues *

Industrial organization In economics, industrial organization is a field that builds on the theory of the firm by examining the structure of (and, therefore, the boundaries between) firms and markets. Industrial organization adds real-world complications to the per ...

, the field of economics that studies the strategic behavior of firms, the structure of markets and their interactions *

Insertion order Insertion may refer to: *Insertion (anatomy), the point of a tendon or ligament onto the skeleton or other part of the body *Insertion (genetics), the addition of DNA into a genetic sequence *Insertion, several meanings in medicine, see ICD-10-PCS ...

, a business document specifying the inventory goal of an advertising campaign *

Integrated operations In the petroleum industry, Integrated operations (IO) refers to the integration of people, disciplines, organizations, work processes and information and communication technology to make smarter decisions. In short, IO is collaboration with focus on ...

, a term used in the petroleum industry describing new work processes and ways of working that have been facilitated by modern information and communication technologies *Interest-only, a type of

collateralized mortgage obligation A collateralized mortgage obligation (CMO) is a type of complex debt security that repackages and directs the payments of principal and interest from a collateral pool to different types and maturities of securities, thereby meeting investor need ...

(CMO) or mortgage-backed security

Language

* i.o., ', Latin phrase meaning "respectively" ("in that order") *

Io (princely title) ''Io'' (Church Slavonic: Ιω, Їѡ and Иѡ, also Iωан and Iωнь; Romanian Cyrillic: Iѡ; ) is the contraction of a title used mainly by the royalty (hospodars or voivodes) in Moldavia and Wallachia, preceding their names and the complete ...

, a particle of a title used by Moldavian and Wallachian Princes-regnant *

Ido language Ido () is a constructed language derived from a reformed version of Esperanto, and designed similarly with the goal of being a universal second language for people of diverse languages. To function as an effective ''international auxiliary ...

(ISO 639-1 language code IO), a constructed language *

Indirect object In linguistics, an object is any of several types of arguments. In subject-prominent, nominative-accusative languages such as English, a transitive verb typically distinguishes between its subject and any of its objects, which can include but ...

, the object that is the recipient of an action (by a verb) * Yo, also referred to as Io

Mythology

, daughter of Inachus in Greek mythology, and lover of Zeus who was turned into a cow *Io, an alternate spelling of the nereid Ino, later known as Leukothea, who in the Odyssey gave Odysseus a veil that allowed him to breathe underwater *

Io Matua Kore Io Matua Kore is often understood as the supreme being in Polynesian native religion, particularly of the Māori people. Io does seem to be present in the mythologies of other Polynesian islands including Hawai‘i, the Society Islands, and th ...

, in some Māori traditions the supreme god

People

*, Japanese shogi player *, Japanese manga artist *

Io Shirai is a Japanese professional wrestler. She is signed to WWE, where she performs on the Raw (WWE brand), Raw WWE brand extension, brand under the ring name (stylized in all caps) and is the current Women's World Championship (WWE), Women’s Wo ...

(born 1990), Japanese professional wrestler *, Japanese manga artist * iO Tillett Wright (born 1985), American artist, director, photographer, writer, film maker, activist, and actor * Jean-Paul Appel, also known as Io, leader of the UFO religion Siderella

Places on Earth

British Indian Ocean Territory The British Indian Ocean Territory (BIOT) is an British Overseas Territories, Overseas Territory of the United Kingdom situated in the Indian Ocean, halfway between Tanzania and Indonesia. The territory comprises the seven atolls of the Chago ...

, ISO 3166-1 alpha-2 code * Io (island), an uninhabited islet near Crete, Greece *

Io, Norway Io is a village in Alver municipality, in Vestland county, Norway. The village sits on the shore of the Herdlefjorden along the northern coast of the island of Holsnøy, about southwest of the village of Rossland. See also *List of short pl ...

, a village in Alver, Norway *

Mount Iō (disambiguation) Mount Iō also Mount Iwo may refer to: * Mount Iō (Akan), in Akan National Park in Hokkaidō * Mount Iō (Iōjima), in Kagoshima prefecture on the island of Iōjima * Mount Iō (Shiretoko), in Shiretoko National Park in Hokkaidō * Mount Iō (Yatsu ...

, name of several mountains in Japan *

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

Science and technology

Astronomy

, a moon of Jupiter *

85 Io 85 Io is a carbonaceous asteroid in the central region of the asteroid belt, approximately 170 kilometers in diameter. It is an identified Eunomian interloper. Discovery and naming It was discovered by C. H. F. Peters on 19 September 186 ...

, an asteroid

Biology and medicine

* ''Io'' (gastropod), a genus of freshwater snail in the family Pleuroceridae * ''Io'' (plant), a genus of plant in the tribe

Senecioneae Senecioneae is the largest tribe of the Asteraceae, or the sunflower family, comprising over 150 genera and over 3,500 species. Almost one-third of the species in this tribe are placed in the genus ''Senecio''. Its members exhibit probably the w ...

*'' Automeris io'', a moth species in North America *''

Aglais io ''Aglais io'', the European peacock, or the peacock butterfly, is a colourful butterfly, found in Europe and temperate Asia as far east as Japan. The peacock butterfly is resident in much of its range, often wintering in buildings or trees. It th ...

'', the European peacock butterfly *

Intraosseous infusion Intraosseous infusion (IO) is the process of injecting medication, fluids, or blood products directly into the bone marrow; this provides a non-collapsible entry point into the systemic venous system. The intraosseous infusion technique is used ...

, the medical process of introducing medication directly into the bone marrow *

Hawaiian hawk The Hawaiian hawk or ''io'' (''Buteo solitarius'') is a raptor in the genus '' Buteo'' endemic to Hawaii, currently restricted to the Big Island. The ''io'' is one of two extant birds of prey that are native to Hawaii, the other being the '' pu ...

() * Immuno-oncology, another term for cancer immunotherapy

Computing

* .io, the Internet country code top-level domain (ccTLD) for the British Indian Ocean Territory *

Io (programming language) Io is a pure object-oriented programming language inspired by Smalltalk, Self, Lua, Lisp, Act1, and NewtonScript. Io has a prototype-based object model similar to those in Self and NewtonScript, eliminating the distinction between instanc ...

, a pure object-oriented programming language * IO.SYS, a system file in Microsoft DOS and Windows 95, 98 and ME *

Indistinguishability obfuscation In cryptography, indistinguishability obfuscation (abbreviated IO or iO) is a type of software obfuscation with the defining property that obfuscating any two programs that compute the same mathematical function results in programs that cannot be ...

, a cryptographic tool to obscure computer code *

Input/output In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs a ...

, the collection of interfaces that different functional units of an information processing system use to communicate with each other

Other uses in science and technology

* Ionium (symbol Io), a claimed chemical element that was later realized to be thorium-230 *

Iodine monoxide Iodine monoxide is a binary inorganic compound of iodine and oxygen with the chemical formula IO•. A free radical, this compound is the simplest of many iodine oxides. It is similar to the oxygen monofluoride, chlorine monoxide and bromine mono ...

(symbol IO) *

Image orthicon tube Video camera tubes are devices based on the cathode-ray tube that were used in television cameras to capture television images, prior to the introduction of charge-coupled device (CCD) image sensors in the 1980s. Several different types of tubes ...

, a TV camera used between 1946 and 1968 *Infinitely often, a mathematics term sometimes written "i.o."; see an example in

set-theoretic limit In mathematics, the limit of a sequence of Set (mathematics), sets A_1, A_2, \ldots (subsets of a common set X) is a set whose elements are determined by the sequence in either of two equivalent ways: (1) by upper and lower bounds on the sequence ...

Other uses

Io (company) io Products, Inc. is an American artificial intelligence hardware company founded in 2024 by Jony Ive, Scott Cannon, Evans Hankey and Tang Tan. The company was acquired by OpenAI in May 2025 to lead its hardware product development. History ...

, an artificial intelligence hardware company * Bureau of International Organization Affairs, in the U.S. Department of State * Government Printing Bureau (Macau), known in Portuguese as the ''Imprensa Oficial'' or "IO" * Indonesian Airlines (IATA airline designator IO) *Investigating Officer, a member of

law enforcement in the United Kingdom Law enforcement in the United Kingdom is organised separately in each of the legal systems of the United Kingdom: England and Wales, Scotland, and Northern Ireland. Most law enforcement duties are carried out by police, police constables of ...

who heads an investigation *

Mitsubishi Pajero iO The Mitsubishi Pajero iO is a mini SUV produced by the Japanese manufacturer Mitsubishi between 1999 (since June 15, 1998, in three-door form, and August 24, 1998, as a five-door) and 2007. The "iO" name is derived from the Italian for "I" which, ...

, a mini SUV model produced by Mitsubishi Motors *

IO (Oral-B) Oral-B is an American brand of oral hygiene products, including toothpastes, toothbrushes, electric toothbrushes, and mouthwashes. The brand has been in business since the invention of the Hutson toothbrush in 1950 and in Redwood City, Calif ...

, a series of electric toothbrushes by Oral-B