1. /ak/ The mnemonic for the ACKnowledge character, ASCII code 6. 2. S> A meSSage tranSmitted to indicate that Some data haS been received correctly. Typically, if the Sender doeS not receive the ACK meSSage after Some predetermined time, or receiveS a NAK, the original data will be Sent again. [Jargon File] (1997-01-07)