Ack is sometimes used as an onomatopoeia for disgust, or as choking on something foul.

ACK as an abbreviation that may refer to:

• ACK (computing), a signal used in computing and other fields to indicate acknowledgement, including:
  • ACK (TCP), a packet message used in the Transmission Control Protocol to acknowledge receipt of a packet.
  • Acknowledge character, a control character used in ASCII.
  • ACK (domain transfer), term used in transfer of domains.
• Acklington railway station (National Rail: ACK), a rail station in the United Kingdom.
• Nantucket Memorial Airport (IATA code: ACK), a Massachusetts airport (referring to Ackerly Field).

ACK as a three-letter acronym that may refer to:

• Amsterdam Compiler Kit, a compiler suite used in Minix.
• Arbeitsgemeinschaft Christlicher Kirchen, a German Christian church.

• Acknowledgment