message authentication code (MAC)
1. A bit string that is a function of both data (either plaintext or ciphertext) and a secret key, and that is attached to the data in order to allow data authentication.
Note: The function used to generate the message authentication code must be a one-way function. [2382-pt.8]
2. Data associated with an authenticated message allowing a receiver to verify the integrity of the message. [INFOSEC-99]