What is the concept of araf?

I have studied about "araf". **It is place between heaven and hell** . I have asked for scholars and there is lot of different views about it . Some say it place for those who did not get to heaven or hell. and some say it is made for those who did not get the massage of Allah from any prophet. I think it is a mystery in Islam. please share your knowledge with me about araf I want to about it.