Roman à clef (said like it rhymes with "a don a day") means "novel with a key" in French. It is a phrase used for talking about literature and movies. A roman à clef is a type of story that's true for the most part except for details like the name of the main character. The "key" part of the meaning–what someone needs to unlock the real story–changes from book to book. For some books it is knowing that the main character is really a famous person. For others it is knowing that the main character is really the author.