Djinn, jinn or as most of us know them ‘genies’ are creatures said to be created of smokeless fire. Like humans, they are male and female, and live in a sort of parallel world to ours where they marry, have children, etc. Sometimes they even marry with humans. So the myth goes.
It is from this Arabic word that our word ‘genius’ comes. They were possibly the earlier ‘peri’ or an Iranian faery, who were also associated with fire. These were part of a group of beings known as tutelary spirits or guides. Thus the word ‘genius’, which is simply a name for a being or someone who knows a lot on a certain subject.