Allegory, from the Greek ἀλληγορία (allegoría) "figuratively", is a literary figure or artistic theme, which aims to represent an idea using human forms, animals, and / or everyday objects.
The allegory aims to give an image to what has no image, so that it can be better understood by the generality. Drawing the abstract, making "visible" what is only conceptual, obeys a didactic intention. Thus, a blind woman with a scale is an allegory of justice, and a skeleton with a scythe is an allegory of death.