In military organizations, the Commander in Chief, also known as the C-in-C, was an official responsible for the overall military organization or organizations.
In the United States of America, the President was the Commander in Chief of all the military forces of that nation. During the later years of the 20th century, the President delegated much of the day to day responsibility for the armed forces to the Secretary of Defense.
The Commander-in-Chief of the Federation Starfleet (also known as C-in-C, Commander Starfleet or Chief of Staff) is a Federation Starfleet Fleet Admiral who is in charge of the overall organization. The C-in-C reports directly to the President of the United Federation of Planets and serves as a primary military advisor to the President and the Council. This person has operational authority over the entire Starfleet.