OO, O_O or variants may refer to:

Look up oo, O O, o O, o o, öö, or Appendix:Variations of "oo" in Wiktionary, the free dictionary.

• OO (EP), by Zion.T, 2017
• OO, production code for the 1967 Doctor Who serial The Ice Warriors
• "O.O" (song), by Nmixx, 2022

• Oô, France
• Oo, Indonesia

• ʻŌʻō, an extinct bird of the genus Moho
• SkyWest Airlines, IATA airline code OO
• OO, the aircraft registration prefix for Belgium
• Old Oak Common TMD, England, carriage shed depot code OO

• several emoticons
• <oo>, a Latin-script digraph
• ‘O‘o stick, a traditional Hawaiian digging bar
• Original Oratory, a competitive event in high school forensic competitions
• OO gauge, a model railway standard
• Official Observer, an appointed amateur radio operator

• Double O (disambiguation)
• 00 (disambiguation)
• 0-0 (disambiguation)
• O0 (disambiguation)
• OOO (disambiguation)
• ${\displaystyle \infty }$, infinity symbol
• ᅇ, an obsolete unit of the Hangul alphabet
• ⚭, marriage symbol
• ⱺ, a phonetic character
• Object-oriented programming, a computer programming paradigm
• Orange Order, a protestant fraternal order in Northern Ireland

This disambiguation page lists articles associated with the title OO.
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