NAO can refer to:

• National Applications Office, an agent of the United States Department of Homeland Security
• National Audit Office in several nations
• Nautical Almanac Office in several nations
• New Age Outlaws, now known as Voodoo Kin Mafia in TNA Wrestling
• North Atlantic oscillation, a climatic phenomenon
• National Academy Orchestra of Canada, a Canadian orchestral training program located in Hamilton, Ontario
• nethack.alt.org, a server for the roguelike game NetHack

Nao can refer to:

• Nao (Japanese name), a Japanese given name
• A Carrack (a three- or four-masted sailing ship developed in the Mediterranean in the 15th century) in Spanish
• Nao, the hero of the Aquablue comic
• Nao, the mascot of the Mabinogi network game.
• Nao (robot), a robot devised by the French company Aldebaran Robotics

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