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

Ethernet address

    (Or "MAC address") The physical address
   identifying an individual Ethernet controller board.  An
   Ethernet addess is a 48-bit number aabbccddeeff where a-f are
   hexadecimal digits.  The first 24 bits, aabbcc, identify the
   manufacturer of the controller.  The Ethernet address is
   hard-wired on some controllers, stored in a ROM on some, and
   others allow it to be changed from software.  It is usually
   written as six hexadecimal numbers, e.g. 08:00:20:03:72:DC.

   See also ARP, Internet address.

   (1996-02-21)