Oni may refer to:

• Oni, Georgia, a town in the Republic of Georgia
• Oni, Uttarakhand, a village in Uttarakhand, India
• Oni (folklore), the demons and ogres of Japanese folklore
  • Oni, a race of aliens from the manga and anime Urusei Yatsura
  • Oni (video game), a third-person shooter video game made by Bungie Studios
  • Oni (鬼), the kanji representing the Challenge difficulty level in Dance Dance Revolution
• Oni Sakti, professional artist, once known as Atticus Ross
• The Oni Aliens, foes in the Gantz manga
• Oni Press, an independent comic book publisher
• Onimusha (series),a series of sequels made by Capcom

ONI may stand for:

• The Office of Naval Intelligence, the United States Navy's intelligence agency
• The National Olympiad of Informatics (Olimpiada Naţională de Informatică), the most important Romanian informatics competition

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