Your spine is made up of vertebrae (bones) and discs (cushion between the bones). The discs are like jelly donuts with a tough exterior and a jelly-like center. When the jelly part escapes from a crack in the touch exterior it is called a herniated disk. People may or may not experience symptoms when this happens. If the escaped jelly irritates nearby nerves it can cause symptoms of pain, weakness, or numbness.

Sources: Mayoclinic.com, Medicinenet.com