Part of the "Megastructures: The Visual Encyclopedia" book project, on sale now at http://www.neilblevins.com/megastructures/megastructures.htm
An Orbital Ring would be an artificial, ring-shaped structure placed around the Earth just above the atmosphere (at 100 km).
The structure would contain two rings. The inner ring would rotate at an angular rate slightly faster than the rotation of the Earth, and would have a current running through it. Then, a second ring would be created that would encompass the first ring, held in place by electromagnets. The second ring would be stationary, and in fact would have fixed tethers that would hang down to the ground. Due to the fact that it would be bound to the orbiting ring, the stationary ring would be held in place above the orbiting ring (this is called an active support structure).