Strictly speaking it is pain along the length of the sciatic nerve, that is down the back of the thigh, through the calf and into the foot. It is sometimes used more loosely to describe any leg symptoms. Achiness that may include tingling, numbness or muscle weakness along the sciatic nerve.
Sciatica is usually caused by pressure on the sciatic nerve from a herniated disc (also referred to as a ruptured disc, pinched nerve, slipped disk, etc.). The problem is often diagnosed as a “radiculopathy”, meaning that a disc has protruded from its normal position in the vertebral column and is putting pressure on the radicular nerve (nerve root).
One or more of the following sensations may occur as a result of sciatica:
Pain in the rear or leg that is worse when sitting
Burning or tingling down the leg
Weakness, numbness or difficulty moving the leg or foot
A constant pain on one side of the rear
A shooting pain that makes it difficult to stand up