If you take a look at answer of that Question you will find why I am saying it is duplicate. It gives you one line answer but I think you want detailed answer on it.
Araf is the Wall between Heaven and Hell. Some says it won't be exact wall as we see usually but it would be Hill between Heaven and Hell. There would be some people whose good and bad deeds would be equal, they will wait for a time and then they will pass through bridge Siraat which is thin like hair and sharp like sword, there they would see Hell at bottom and Heaven in-front.
There are some ayah from Surah Al'Araf which are related to araf.
And between them will be a partition, and on [its] elevations are men who recognize all by their mark. And they call out to the companions of Paradise, "Peace be upon you." They have not [yet] entered it, but they long intensely.
Surat Al-'A`rāf - 46
And when their eyes are turned toward the companions of the Fire, they say, "Our Lord, do not place us with the wrongdoing people." Surat Al-'A`rāf - 47
This should clear your mind about Araf.