Wyrme, Ouroborous and Spaghetti, topopli in the Cableville system
Long, thin, rotating habitat in orbit around a star or planet, so that the long axis of the habitat passes completely around the orbit at least once. If the short radius of loop is very much smaller than the long radius, then the difference between the inside and the outside radius of the loop is negligible, and the hoop can rotate without noticeable internal distortion.
Also called a 'macaroni world'. First suggested by Information Age fabulist Larry Niven.