A reference to another literary text, poem, or mythological story is an allusion.
Allusion refers to a brief reference to a person, place, event or to another literay work made in a piece of writing or literary work. Allusion was very common in classic and romantic poetry which had many references to ancient mythology.
Allusion is just a passing comment and the writer expects the reader to have broad knowledge to spot the allusion and comprehend its importance in a text.
