Discs are small circular, compressible cushions between the vertebral bones in the spinal column. They act as cushions for the vertebrae. A herniated disc bulges from its proper place, putting pressure on spinal nerves. This is most common in the lower spine.

Herniated Lumbar Disc
Nucleus factsheet image
Copyright © Nucleus Medical Media, Inc.

A herniated disc is caused by reduced water content, which results in flattening and less cushioning. It can also be the result of trauma.