A Roman à Clef novel is one which is based on true characters, portrayed in true settings, in a thinly veiled narrative. It means a novel with a key in French.Many modern Indian novels are based on characters whose personalities are very slightly masked in this manner.
I wandered into this territory after researching about Hemingway's novel "The Sun Also Rises." I remember being inspired enough to want to be a writer of novels. For a detailed explanation go to this Wikipedia article.