Sciatica refers to pain felt along the length of the sciatic nerve. The pain is usually felt in the buttocks, where it radiates down the leg. If you suddenly start feeling pain in your lower back or hip that radiates to the back of your thigh and into your leg, you may have a protruding (herniated) disc in your spinal column that is pressing on the roots of the sciatic nerve. This condition is known as sciatica.
Quite often, leg pain or foot pain does not mean that there is a problem with the leg or foot, but rather that there is a problem in the lower back, causing pain and possibly other symptoms to radiate, or be referred to, the leg or the foot.
An important thing to understand is that sciatica is a symptom of a problem - of something compressing or irritating the nerve roots that comprise the sciatic nerve - rather than a medical diagnosis or medical disorder in and of itself. This is an important distinction because it is the underlying diagnosis (vs. the symptoms of sciatica) that often needs to be treated in order to relieve sciatic nerve pain.