What is a jinn?

As far as I know, a Jinn is of a race that Allah has made out of (pure, smokeless) fire just like humans where made by Him out of clay. Reading recent questions, and old ones "botted up" by the Community Bot, most of them looking like asking for personal advice, often asking about jinns. I cannot help but feel that there is some misunderstanding of jinns in common folklore and what is really based on Islam. From the questions, it looks like jinns are looked on as a kind of devils, bringing harm, bad luck and nightmares. From my very, very bad translation of the Quran I once had I remember a Sura where Prophet Muhammad stated that when he was speaking, there was also a number of jinns present. So they cannot be all that bad, not all of them. Sorry if I can't make a clear and unambiguous question out of my thoughts. I will sharpen it if someone can direct me.