While herniated discs are often referred to as “slipped discs,” this really isn’t accurate because discs don’t ever slip out of position. They are actually attached by connective tissue to vertebrae above and below. A disc herniation can be “contained” or “uncontained.” With a bulge, for example, the jelly center remains within the disc wall. "Uncontained" means the jelly center has broken through the annulus wall but stays connected to the nucleus pulposus. Or the herniation can be “sequestered,” when it breaks free from the nucleus and travels away from the disc.
A bulging disc forms when the wall of the disc is deformed but not necessarily herniated. The nucleus is still contained in the wall. You NEVER need surgery to treat a bulging disc.