What is the difference between a disc bulge and slipped disc (disc herniation)?

The disc has a tough fibrous outer ring (annulus) and a softer core (nucleus pulposus, NP) that cushions the spine when we jump. With degeneration of the spine, the annulus weakens and gradually tears allow the NP to push its way out towards the spinal canal. With a weak annulus, the disc will bulge backwards into the spinal canal and may narrow the canal and cause compression on the spinal cord or nerve roots. When the annulus is completely torn, the NP will be able to slip ( or herniate, prolapse) out causing more severe compression resulting in severe pain, tingling and even weakness in the arms or legs.