Stories that are supposed be short and about a parallel and imaged world, which does not exist.
Other world can be whatever you want.
A: Have you read the story about buying "free" time?
B: Oh yeah!
It is a great concept story.
The craziest stories the world has heard.
It can come from either your imagination or dreams.
I had the craziest idea right now! Maybe I should write a concept story!