Pain radiating down the leg from pressure on the sciatic nerve is called sciatica.
The sciatic nerve is the body’s largest nerve. It forms from nerve roots in the lower spine, passes through the buttock, and travels down the back of the leg. When one of those nerve roots is irritated or compressed, often by a herniated spinal disk, the resulting pain can follow that pathway.
Sciatica is usually a symptom rather than a disease with one single cause. Besides disk herniation, possible causes include spinal stenosis, spondylolisthesis, and piriformis syndrome. The pain may feel sharp, burning, or electric, and it can occur with numbness, tingling, or weakness.
A common mix-up is calling any lower-back pain sciatica. Sciatica generally involves pain that travels into the buttock and leg, often below the knee; pain confined to the lower back is not typically described as sciatica. Most cases improve within weeks, but sudden bowel or bladder problems or severe weakness require urgent medical attention.