Io, IO, iO, I/O, i/o, or i.o. may refer to:

  • Io (mythology), daughter of Inachus in Greek mythology, and lover of Zeus who was turned into a cow
  • Io (moon), a moon of Jupiter

In arts and media

Fictional elements



Theatre and opera

  • Io (opera), an unfinished acte de ballet (opera) by Jean-Philippe Rameau
  • iO Theater (ImprovOlympic), a theater in Chicago, Illinois, dedicated to improvisational comedy
  • IO West, a Los Angeles theater associated with the Chicago iO

Other uses in arts and media

Businesses and organizations

In business and economics


  • i.o., in illo ordine, Latin phrase meaning "respectively" ("in that order")
  • Io (princely title), a particle of a title used by Moldavian and Wallachian Princes-regnant
  • Ido language (ISO 639-1 language code IO), a constructed language
  • Indirect object, the object that is the recipient of an action (by a verb)


  • 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, in some Māori traditions the supreme god


  • Io Murota (室田 伊緒, born 1989), Japanese shogi player
  • Io Shirai (born 1990), Japanese professional wrestler
  • iO Tillett Wright (born 1985), American artist, director, photographer, writer, film maker, activist, and actor


Science and technology


Biology and medicine


  • .io, the Internet country code top-level domain (ccTLD) for the British Indian Ocean Territory
  • Io (programming language), a pure object-oriented programming language
  • IO.SYS, a system file in Microsoft DOS and Windows 95, 98 and ME
  • Indistinguishability obfuscation, a cryptographic tool to obscure computer code
  • Input/output, 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
  • Image orthicon tube, a TV camera used between 1946 and 1968
  • Infinitely often, a mathematics term sometimes written "i.o."; see an example in set-theoretic limit

Other uses

See also