"The new version of TECO quickly became popular at the AI Lab and soon accumulated a large collection of custom macros whose names often ended in MAC or MACS, which stood for macro. Two years later, Guy Steele took on the project of unifying the diverse macros into a single set.[21] Steele and Stallman's finished implementation included facilities for extending and documenting the new macro set.[3] The resulting system was called EMACS, which stood for Editing MACroS or, alternatively, Emacs with MACroS."
"The new version of TECO quickly became popular at the AI Lab and soon accumulated a large collection of custom macros whose names often ended in MAC or MACS, which stood for macro. Two years later, Guy Steele took on the project of unifying the diverse macros into a single set.[21] Steele and Stallman's finished implementation included facilities for extending and documenting the new macro set.[3] The resulting system was called EMACS, which stood for Editing MACroS or, alternatively, Emacs with MACroS."
https://en.wikipedia.org/wiki/Emacs