A brief reference, without explanation, to a person, text, myth, or fact known outside the work, which carries with it the meaning of that other story.
In Julius Caesar
I, as Aeneas, our great ancestor, / Did from the flames of Troy upon his shoulder / The old Anchises bear, so from the waves of Tiber / Did I the tirèd Caesar
Cassius calls Aeneas "our great ancestor" and mentions old Anchises carried out of the flames of Troy without telling the story, as if the Roman listener knew it. The reference gives his gesture the weight of legend.