Sciatica describes any pain or neuropathy of the five sciatic nerves at the base of the spine due to compression or irritation that usually appears on only one side. Although it's often thought of as a disease, in fact it merely describes a set of symptoms that can be caused by a number of underlying causes, most commonly a herniation of a spinal disc or hardening of the spine.
In most cases, identifying sciatica allows a physician to treat the symptoms while looking for a way to properly treat the underlying cause. Most cases are self resolving and painkillers should be avoided as they are usually ineffective, particularly over the long term. Surgery is usually not recommended due to the risks involved, which provide little hope of benefit in most cases. Moderate exercise is usually the best course of action, although bed rest may also be recommended.