Allusion is a literary device that refers to a brief and indirect reference to a person, place, thing, or idea of historical, cultural, literary, or political significance. It relies on the reader's familiarity with the referenced subject to convey deeper meaning or context. Allusions can enrich a text by adding layers of meaning, evoking emotions, or drawing connections between different ideas. They are often used in poetry, prose, and speeches to enhance the message without lengthy explanations.