Root canal is a treatment to repair and save a badly damaged or infected tooth instead of removing it. The procedure involves removing the damaged area of the tooth (the pulp) and cleaning and disinfecting it, then filling and sealing it. The common causes affecting the pulp are a cracked tooth, a deep cavity, repeated dental treatment to the tooth or trauma to it. The term "root canal" comes from cleaning of the canals inside the tooth's root.
Decades ago, root canal treatments were painful. With dental advances and local anesthetics, most people have little if any pain with a root canal today.