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 Notes from Underground
I even cried, although I knew with complete exactness, at that very moment, that all of it came from Silvio and from Masquerade, by Lermontov.
The sentence points, without explaining, to two literary sources: «Silvio» and «Masquerade, by Lermontov». By naming the books from which he took the script, the narrator confesses that his revenge is a scene from reading and not from life.