"Filk music is a musical movement among fans of science fiction and fantasy fandom and closely related activities, emphasizing content which is related to the genre or its fans, and promoting broad participation. Filkers are people who participate in this movement." -- Gary McGath
Many people wondered what Leonard Nimoy was trying to accomplish when he recorded his "Ballad of Bilbo Baggins" years ago. While the world my never know his intentions, the result seems to be the genesis of the filk movement.