A Root Canal is a treatment used to repair and save a tooth that is badly decayed or becomes infected.

During a root canal procedure, the nerve and pulp are removed and the inside of the tooth is cleaned and sealed. Without treatment, the tissue surrounding the tooth will become infected and abscesses may form.
"Root canal" is the term used to describe the natural cavity within the center of the tooth. The pulp or pulp chamber is the soft area within the root canal. The tooth's nerve lies within the root canal - WebMD