The Montreal Urban Community Transit Corporation operated the public transportation network for the Montreal region. It managed the integration of bus routes, commuter trains, and the Metro system across the metropolitan area. The agency underwent several name changes as regional governance evolved, eventually being reorganized and replaced by the current transit authority.
I found some old MUCTC route maps in the archives showing the original Metro line extensions.
Transit historians and veteran operators still use this acronym when referring to the older rolling stock and historic station designs implemented under its administration.