Jinn literally means something invisible. Snakes are called Jaan in arabic. This is because they usually are hidden from the eye. Quran describes Jinn in various contexts. The word is applied to different entities, groups or persons according to the context.
Shaitan, means the one who rebels, an adversary, a disobedient person. Iblees is called Shaitan because he rebelled. He is also desribed as being among the Jinns. Quran also uses this word in plural, shayateen.
Many people believe that Jinns are similar creatures like genies, demons, spirits etc, but Quran does not support this view. Jinns can be humans as well as animals. Tribes and nations who lived in the mountains, and remote places were called Jinns. Invisible creatures like bacteria and viruses are also called Jinn. People of rebellious nature are also called Jinn.
Shayateen are the opposite of angels. But they do not inhabit people and disturb them as popularly believed. Again, shayateen can be humans too, who cause hurdles in the way of truth and oppose the message of God.