When you have a prolapsed disc (commonly called a slipped disc). A disc does not actually slip. What happens is that part of the inner softer part of the disc (the nucleus pulposes) bulges out through a weakness in the outer part of the disc. A prolapsed disc is sometimes called herniated disc. The bulging disc may press on nearby structures such as a nerve coming from the spinal cord. Some inflammation also develops around the prolapsed part of the disc.
Any disc in the spine can prolapse. However, most prolapsed discs occur in the lumbar part of the spine (lower back). The size of the prolapse can vary. As a rule, the larger the prolapse, the more severe the symptoms are likely to be.