They are brief but impactful. For instance, the story of the girl and the flower. It doesn't take long to tell. The characters in such stories are usually archetypal, like the girl representing someone with self - control. And the moral is often something that is timeless, like respecting nature, which is relevant in any era.
Well, one characteristic is that it has a simple plot. For example, like the story of the boy who cried wolf, it's easy to follow. Another is that it has a clear moral. In the wolf story, the moral of not lying is very straightforward. Also, it usually involves only a few characters. Just the boy and the villagers in that story.