NAK is the negative-acknowledge character used in computers and telecommunications.
NAK or Nak may also refer to:
- Nak, Hungary
- NaK, an alloy of sodium and potassium metals
- Mae Nak Phra Khanong, a ghost of Thai folklore
- Nak (film), a 2008 animated film based on the Thai ghost
- Ningalkkum Aakaam Kodeeshwaran, a quiz show in Malayalam based on Who Wants To Be A Millionaire?
- NAK, the IATA airport code for Nakhon Ratchasima Airport