Allegory vs. Parable
Apparently, not that big of a difference. According to Wikipedia, a parable is
Parable and allegory are often treated as synonyms, but are well distinguished by H. W. Fowler, in Modern English Usage. "The object in each" said Fowler, "is to enlighten the hearer by submitting to him a case in which he has apparently no direct concern, and upon which therefore a disinterested judgment may be elicited from him." It then dawns upon the listener or reader that the conclusion applies equally well to his own concerns.while an allegory
is a figurative representation conveying a meaning other than and in addition to the literal. It is generally treated as a figure of rhetoric, but an allegory does not have to be expressed in language: it may be addressed to the eye, and is often found in painting, sculpture or some form of mimetic art. The etymological meaning of the word is wider than that which it bears in actual use. An allegory is distinguished from a metaphor by being longer sustained and more fully carried out in its details, and from an analogy by the fact that the one appeals to the imagination and the other to the reason. The fable or parable is a short allegory with one definite moral.