negative acknowledge; NAK
Technical term in data communication: a signal sent to indicate that a message was received with errors or cannot be accepted. Often abbreviated as NAK.
If the receiver returns a negative acknowledge, the sender retransmits the data.
Positive acknowledge (ACK), the opposite signal indicating successful receipt.
Compound of 否定 (negation) and 応答 (response), likely a calque from English 'negative acknowledge'.