Saturn's rings are a conglomeration of myriad lumps of ice and dust orbiting in a very tight plane, appearing as discs. There is considerable structure to the rings, caused by the pull of Mimas and the influence of several small shepherd moons that orbit either side of a ring, keeping it in line.
Saturn's rings are the most prominent in the Solar System, although the other gas giants (Jupiter, Uranus and Neptune) have all been found to have rings to some extent.