A herniated disk is when a crack in a spinal disk causes back pain, according to the Mayo Clinic.

Spinal disks – which are rubbery cushions between the vertebrae – protect the vertebrae from rubbing against each other, the Mayo Clinic states.

As people age, there is less water in the outer layer of each disk, making the disk less stretchy and more likely to crack, according to the Mayo Clinic. When it cracks, or herniates, the nucleus can come out and press on nerves, which will cause back pain.