mac

(1) See Macintosh, MAC layer, MAC address, moves-adds-changes and mandatory access control.

(2) (Message Authentication Code) A number computed from the contents of a text message that is used to prove the integrity of a message. The MAC is a checksum that is computed using an algorithm based on the DES or AES ciphers, which use a secret key. The MAC is then sent with the message. The recipient recomputes the MAC at the other end using the same algorithm and secret key and compares it to the one that is sent. If they are the same, it is assumed that the message has not been tampered with.

A MAC is like a digital signature, except that a secret key is used rather than a private key. Also known as the U.S. Government Standard Data Authentication Code (FIPS PUB 113). See digital signature, cryptography and DES.

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In anesthetics, minimum alveolar concentration; in immunology, membrane attack complex.

The noun has one meaning:

Meaning #1: (British) a waterproof raincoat made of rubberized fabric
  Synonyms: macintosh, mackintosh, mack