Method of expressing complex or abstract ideas in the literary or visual arts under the guise of another subject of aptly suggestive resemblance. An allegory is principally constructed from personifications and symbols. In art, allegories include combinations of personifications and/or symbols, which, on the basis of a conventionally agreed relation between concept and representation, refer to an idea outside the work of art. The properties and circumstances attributed to the apparent subject of the allegory really refer to another subject in an extended or continued metaphor. Allegories may have meaning on two or more levels that the viewer or reader can understand only through an interpretive process.

Source:  Art & Architecture Thesaurus

http://vocab.getty.edu/page/aat/300055866