Allusion

An allusion is "a figure of speech that makes a reference to someone or something" without naming it or explaining the connection, leaving the audience to complete the link. The writer's risk is the article's social fact: "an allusion is understandable only to those with prior knowledge of the covert reference in question," and "without the hearer or reader comprehending the author's intention, an allusion becomes merely a decorative device." The examples run from Homer's epics and Virgil's Georgics to The Waste Land, and to Martin Luther King Jr. reaching back to the Gettysburg Address with "Five score years ago."

Allusion is a contract with a readership: it rewards those who catch it and quietly passes over those who do not. In worldbuilding it buys depth cheaply, a history implied rather than told, and a story leaning hard on borrowed resonance drifts toward parody or, uninvited, fan fiction.