Dictionary: Allegory

Allegory:

Allegory is a representation of an abstract or spiritual meaning through concrete/material forms. It is the figurative treatment of one subject under the guise of another. George Orwell's book, Animal Farm, for example, is an allegory. Orwell represents revolutions in general, and most specifically the Russian revolution, through the revolt of the farm animals.

Chaucer's A Knight's Tale, found in The Canterbury Tales, has been interpreted/suggested as allegory. For example, the characters Arcite and Palamon are thought to represent the active and contemplative life.

Beware, however, when writing allegorical fiction. All too often writers have abstract ideas, but no story. If that is the case, then your allegorical fiction will be a bunch of talking ideas. In good fiction, the ideas do not drive the story, the story drives the ideas.

Flannery O'Connor, author of Wise Blood and The Violent Bear it Away (among bunch of other famous short stories, essays, and letters), says this about the importance of concrete story over abstract idea:

"They [people who want to write stories] want to write about problems, not people; or about abstract issues, not concrete situations. They have an idea, or a feeling, or an overflowing ego, or they want to Be A Writer, or they want to give their wisdom to the world in a simple-enough way for the world to be able to absorb it. In any case, they don't have a story and they wouldn't be willing to write it if they did; and in the absence of a story, they set out to find a theory or a formula or a technique. (Flannery O'Connor, Mystery and Manners)"

The point O'Connor is trying to express is that ideas do not drive a story. Accuracy (a previous dictionary term), drives the story. What the eye sees from the provided details drives a story. From those concrete details comes ideas.