U+2415 "␕" Symbol for Negative Acknowledge Unicode Character

U+2415 "␕" Symbol for Negative Acknowledge is a control code graphic used in computing and telecommunications to visually represent the ASCII control character NAK, which has a numerical value of 21. Originally defined in the C0 control code set, the NAK character was part of the early communication protocols for data transmission, where it indicated that the receiving device did not correctly receive the previous block of data and requested a retransmission. The graphic symbol itself, depicting the letters "NAK" enclosed in a single-line box, was introduced in Unicode to allow for the visible printing or display of this non-printable control code, making it useful in debugging, logging, and data analysis contexts where the actual control function needs to be represented as a tangible character.