A novel with a key -- roman à clef

from www.wordsmith.org

roman à clef (ro-mahn ah KLAY) noun, plural romans à clef
A novel that depicts (usually famous) real people and events under the guise of fiction.
[From French roman à clef, literally, a novel with a key.]

All fiction has a grain of truth, but a roman à clef has it by the bushel. Roman à clef dates back to seventeenth century France. In the beginning, a roman à clef really did have a key that was published separately. In these times, you can simply go on the Internet and search using Google.
An example of roman a clef is Ernest Hemingway's The Sun Also Rises. These days the term can apply to any work of fiction, for example, a movie, not just a novel. A blend term "faction" has also been used, after "fact"presented as "fiction".

"[Geraldine] Brooks has borrowed details not just from Little Women but from the story of Alcott's own extraordinary father, Bronson Alcott, a man whose free-thinking, utopian views were all downplayed in his daughter's roman à clef."
-- Michelle Griffin; March; Sydney Morning Herald (Australia); Apr 2, 2005.