Allegory is a term of long history, wide use and likely vagueness in literary criticism and Persian eloquence. The term is sometimes used as the synonym of symbol, parable, and anecdote. In this article, an attempt has been made to explore the eloquent author's definitions in both old and new literary criticism and Persian eloquence by studying the background of allegory in religious literature and myths. The nature, function and types of allegory will be explored as well. Finally, the differences between metaphor and symbol of allegorical domains will be discussed.