ACI

• Aero Club of India, the apex body of all flying clubs and the governing body for air sports in India
• Aircalin, an airline (ICAO code: ACI)
• Air Cargo Inc., an organization that provides information to the freight forwarding industry
• Airports Council International, international trade group of the world's commercial aviation industry, based in Montreal, Canada
• Aviators Code Initiative, an organization advancing flight safety and professionalism
• Aviazione Cobelligerante Italiana, the air force of the Royalist "Badoglio government" in southern Italy during the last years of World War II
• IATA airport code for Alderney Airport in Guernsey

• Agincourt Collegiate Institute a secondary school located in Toronto, Canada
• Albertson College of Idaho, now known as the College of Idaho, a small liberal-arts college in Idaho
• American Collegiate Institute, Izmir Amerikan Lisesi, located at İzmir, Turkey

• Alternate Concepts, a transportation management company in the United States

• ACI (conglomerate), one of the largest Bangladeshi conglomerates
• ACI Worldwide, a payments software company
• Adriatic Croatia International Club, a chain of marinas in Croatia
• Albertsons Companies, Inc., an American supermarket chain
• American Concrete Institute, a non-profit standards-developing organization
• American Constitutional Initiative, a non-profit organization that promotes progressive change
• Anti-Corruption Ireland, political group created by Gemma O'Doherty
• Arch Coal inc., A major U.S. coal mining company
• Aurora Cable Internet, a digital cable television, cable internet and VOIP provider in Aurora, Ontario
• Automobile Club d'Italia, a member of the Fédération Internationale de l'Automobile

• Aci Castello (Sicilian: Jaci Casteddu), a city and comune in the Province of Catania in Sicily, Italy
• Acı, Pasinler
• Acireale, Sicilian city sometimes abbreviated Aci
• Jaci (river), also called the Aci

• Adjacent-channel interference, power from a signal in an adjacent channel
• An alternate name for the nitronate moiety
• Application container image, a specification for the format and environment of virtualization containers, initiated by CoreOS
• Autologous chondrocyte implantation, a medical treatment for articular cartilage damage
• Automatic Car Identification, a railroad barcode system that preceded the automatic equipment identification
• Cisco Application Centric Infrastructure, Cisco's implementation of software-defined networking

• Accusative and infinitive a.k.a. accusativus cum infinitivo, a construction in Latin grammar
• Ace Combat Infinity
• Acis (Italian: Aci) of Acis and Galatea in Greek mythology
• Air Crash Investigation, an alternate name for the television series Mayday
• Aka-Cari language, an extinct Great Andamanese language
• American Competitiveness Initiative, a federal program intended to help America maintain competitiveness
• Assassin's Creed I, the first entry in the long-running Assassin's Creed series.

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