The Free On-line Dictionary of Computing (30 December 2018):

Media Access Control
Medium Access Control

    (MAC) The lower sublayer of the OSI data link
   layer.  The interface between a node's Logical Link
   Control and the network's physical layer.  The MAC differs
   for various physical media.

   See also MAC Address, Ethernet, IEEE 802.3, token ring.

   [What does it do?  Examples?]

   (1996-01-29)