OA

• Oa (comics), a fictional planet in the DC Comics universe
• The OA, a television series
• OpenArena, a video game
• Opie and Anthony (often "O&A"), a radio show
• Oriental Adventures, a Dungeons & Dragons sourcebook
• Orion's Arm, a science fiction project

• Obavještajna agencija, the Croatian Intelligence Agency
• Office administration
• Oficina Anticorrupción, an Argentine law enforcement agency
• Olympic Air (IATA code OA)
• Opera Australia, an opera company
• Opportunitas aequa, a Canadian organization
• Overeaters Anonymous
• Oxford Academy (California), a high school
• Orbital ATK, an aerospace company

• Ma'am OA, nickname of Andrea Veneracion, founder of the Philippine Madrigal Singers
• Oskar Andersson, Swedish cartoonist who uses the pen name O.A.

• Oa (Attica), a deme of ancient Attica
• Ocean Acres, New Jersey, United States
• Orakzai Agency, Pakistan
• The Oa, Scotland, United Kingdom

• Order of Australia, a formal honour
• Order of the Arrow, the honor society of Scouting America

• Office automation
• Oleic acid, a fatty acid
• Open access, the free online availability of digital content from scholarly sources
• Operational amplifier, an electronic component
• Operational analysis, more generally called "operational research", a branch of applied mathematics
• Osteoarthritis, a disease
• Length overall (also o/a, o.a. or oa), an abbreviation for overall, used when describing the length of a ship
• Oxford Archaeology

• Oa (digraph)
• Obituaries Australia, an online database of obituaries
• Office Action, a communication from the U.S. Patent and Trademark Office
• Old Alleynian, an old boy of Dulwich College
• Old Albanian, an old boy of St Alban School, St Albans
• Order of Appearance, a synonym for Order of battle
• Output area, an area of approximately 100 households, derived from the UK Census

• 0A (disambiguation)
• OOA (disambiguation)

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