WikiPedia's definition of a fable is so good, it seems impossible to be improved upon, so giving them full credit and a link here in the related links section below, this is a quote of their definition:
A fable is a succinct story, in prose or verse, that features animals, plants, inanimate objects, or forces of nature which are anthropomorphized (given human qualities), and that illustrates a moral lesson (a "moral"), which may at the end be expressed explicitly in a pithy maxim.
Some of the more famous fables, Aesop's Fables, include:
- The Fox and the Grapes
- The Tortoise and the Hare
- The North Wind and the Sun
- The Boy Who Cried Wolf