microfiction
A short story, usually no more than 300 words, becoming more and more popular on the Internet. One suspects that the technology of portable readers has helped this genre along. Also known as "flash fiction." Wikipedia offers Aesop's Fables as some of the earliest and best-known microfictions.
One ancient and respected microfiction is Aesop's "The Fox and the Grapes," whence we get the expression "sour grapes."