A brief reference, without explanation, to a person, a text, a myth or a fact known outside the work, which carries with it the meaning of that other story.
In Madame Bovary
Read Voltaire! [...] Read Holbach, read the Encyclopédie!
Voltaire, Holbach and the Encyclopédie refer to authors and a work known outside the novel. Cited without explanation, they show that Homais defends his ideas by the prestige of names, and not by the content of what he discusses.