Between each pair of spinal bones is a disc. Its fibrous outer ring holds in a jelly-like material. This soft center serves as a “ball bearing” for joint movement. Because of the way a disc attaches to the spinal bones above and below it, it can’t actually “slip”. However, a disc can bulge. It can tear. It can herniate. It can thin. It can dry out. And it can collapse. But it can’t slip.