“Project MAC” was a project at the Massachusetts Institute of Technology (MIT) started in the 1970s. KentPitman says “The acronym MAC stood for no particular thing, but various meanings were attached, such as: Men and Computers, Minds and Cognition, Machine-Aided Cognition, etc.”
In his excellent book “Hackers, heroes of the computer revolution” (see HackersTheBook) Steven Levy writes:
Project MAC, and in particular the MIT AI Lab, was the environment which spawned TecoEmacs.