A figurehead was a ruler who had little power but symbolic value.
In 2369, Worf suggested that although the clone of Kahless would be a figurehead, his presence as Emperor of the Klingon Empire would go a long way towards returning honor to the Klingon people. (TNG: "Rightful Heir")
In 2372, Kor called this clone a "toothless figurehead", saying that the Sword of Kahless would only be able to unite the Klingon people if held by a warrior like Kang and Koloth. (DS9: "The Sword of Kahless")