The Free On-line Dictionary of Computing (30 December 2018):
Project MAC
    A project suggested by J C R Licklider; its founding
   director was MIT Prof. Robert M Fano.  MAC stood for
   Multiple Access Computers on the 5th floor of Tech Square, and
   Man and Computer on the 9th floor.  The major efforts were
   Corbato's Multics development and Marvin Minsky's
   Artificial Intelligence Laboratory.  In 1963 Project MAC
   hosted a summer study, which brought many well-known computer
   scientists to Cambridge to use CTSS and to discuss the
   future of computing.
   Funding for Project MAC was provided by the Information
   Processing Techniques Office of the Advanced Research
   Projects Agency (ARPA) of the US Department of Defense.
   See also Early PL/I, MacLisp, MACSYMA, MDL,
   Multipop-68, OCAL.
   (1997-01-29)