from
The Free On-line Dictionary of Computing (8 July 2008)
negative acknowledgement
1. <character> (NAK) The {mnemonic} for {ASCII} character 21.
Sometimes used as the response to receipt of a corrupted
{packet} of information.
Opposite of {acknowledgement}.
2. <communications> (NAK) Any message transmitted to indicate
that some data has been received incorrectly, for example it
may have a {checksum} or message length error. A NAK message
allows the sender to distinguish a message which has been
received in a corrupted state from one which is not received
at all.
An alternative is to use only {ACK} messages, in which case
the non-receipt of an ACK after a certain time is counted as a
NAK but gives no information about the integrity of the
communications channel.
See also {ACK}.
(1997-01-07)