- ACK stands for Amar Chitra Katha (Indian entertainment company)
- ACK stands for Akademickie Centrum Kultury (Polish: Academic Center for Culture; Lublin, Poland)
- ACK stands for Arbeitsgemeinschaft Christlicher Kirchen (German: Council of Christian Churches)
- ACK stands for Acknowledgement Packet
- ACK stands for Acknowledge Character
- ACK stands for Anglican Church of Kenya
- ACK stands for Amsterdam Compiler Kit
- ACK stands for Nantucket, MA, USA (Airport Code)
- ACK stands for Assistant Cook (US DoD)
- ACK stands for Accounting Control Key
- ACK stands for America’s Career Kit (US Department of Labor)
- ACK stands for Aircraftkiller (gaming)
- ACK stands for Acknowledged Signal (mobile radio communication system)
- ACK stands for Anti-Capitalist Kananaskis (counter G8 movement)
- ACK stands for Acknowledge/Acknowledgement/Acknowledged
ACK