An Allegory as M.H. Abrams says,"is a narrative in which the agents and action and sometimes the setting as well are contrived not only to make sense in themselves but also to signify a second, correlated order of persons, things, concepts or events."
Allegories are of different types like historical or political allegory, the allegory of ideas and moral allegory. Dryden's "Absalom and Achitophel" may be considered as historical or political allegory.
Bunyan's "Pilgrim's Progress" is a moral or religious allegory. Spenser's "Faerie Qqueen" can be considered as a moral, religious, historical and political allegory.
The political allegory is within the framework of the moral allegory. Alex Preminger says, "An Allegory may be simple or complex. In simple allegory the fiction is wholly subordinate to the abstract 'moral'. The complex historica and politicl allegories tend to develop a strongly ironic tone.
Morality plays are distinctly allegorical. As M.H. Abrams says, "Morality plays are dramatised allegories of the life of man, his temptation and sinning, his quest for salvation, and his confrontation by death."
Allegory is a figurative mode of representation conveying meaning other than the verbal. Allegory communicates its message by means of symbolic figures, actions or symbolic representation. Allegory is generally treated as a figure of rhetoric, but an allegory does not have to be expressed in language: briefly, an allegory is a device used to present an idea, principle or meaning, which can be presented in literary form, such as a poem or novel, or in visual form, such as in painting or drawing.