One cause of back pain is when a disc buldge or herniation causes the disc to touch a spinal nerve.

As the name implies, disc buldge means that some part of the disc is bulging (compared to its original structure).

Disc herniation mean there is a bigger buldge (loosely speaking). Disc buldge refers to a buldge of the outer ring (annulus fibrosus) but the nucleus pulposus remains contained by annulus fibrosus. When the gel-like nucleus pulposus breaks trough the tough outer annulus fibrosus, the condition is called disc herniation.

Disc buldge and herniation may result in back pain and pain or sensations down the legs.