A roman à clef or roman à clé (French for "novel with a key") is a novel describing real-life events behind a façade of fiction. The "key", not present in the text, is the correspondence between events and characters in the novel and events and characters in real life.
Reasons why an author might choose the roman à clef format include:
Writing about controversial topics and/or reporting inside information on scandals without giving rise to charges of libel.
A roman à clef also gives the author the opportunity to turn the tale the way the author would like it to have gone.
Since its original use in the context of writings, the roman à clef technique is also used in the theatre and in movies, like The Great Dictator depicting Hitler and nazism.
Some notable romans à clef:
Virtually all of the novels of Thomas Love Peacock (1785 - 1866) presuppose a knowledge of English intellectuals and currents of thought of the time.
Glenarvon (1816) by Lady Caroline Lamb which chronicles her affair with Lord Byron (thinly disguised as the title character).
The Blithedale Romance by Nathaniel Hawthorne depicts the participants in the Brook Farm experiment, under the veil of a story about the search for a magic elixir.
The Lady of Aroostook depicts Emily Dickinson's romantic engagements with several men.
In the season 4 X-Files episode Musings of a Cigarette Smoking Man, the recurring villain known as the Cigarette Smoking Man moonlights as author Raul Bloodworth and is published in a sleazy rag called Roman A Clef. The name is ironic in the context, as what he has sent to the magazine is indeed a roman à clef account of the secret conspiracies he has been involved in, but the magazine's editors rewrite it until it's unrecognizable.
The French term roman à clef loosely translated means a novel that needs a key to unlock it. For a full understanding of such novels it is necessary for the reader to know something of the events or characters that inspired it, though this information may not be provided by the book itself.
The word clef comes from the French, meaning key. In music notation, the symbol is placed at the beginning of the staff, setting a reference for, or giving a key to, all notes of the staff.
Since its original use in the context of writings, the roman à clef technique is also used in the theatre and in movies, like The Great Dictator depicting Hitler and nazism.
Roman à clef is one of the many dimensions of Orlando: A Biography (1928) by Virginia Woolf.