Secretary-General is a title many different organizations give to their leader.
The United Nations Secretary-General is described as the chief administrative officer and the De facto head of the United Nations. The Office of the Secretary-General of the United Nations hires, terminates, and controls all United Nations staff and relief efforts around the World.
The Commonwealth of Nations also calls their De facto leader Secretary-General. The Secretary-General advises member nations and heads conferences with the Head of the Commonwealth, currently Queen Elizabeth II. The monarch of the United Kingdom is the ex officio Head of the Commonwealth of Nations.
The Secretary-General of the North Atlantic Treaty Organization (NATO) is the chief administrative officer of NATO and supreme commander of NATO forces when mobilized.
International intergovernmental organizations 
International nongovernmental organizations 
Sports governing bodies 
See also