A root canal is the space within the root of a tooth

Tooth

Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

. It is part of a naturally occurring space within a tooth that consists of the pulp chamber (within the coronal part of the tooth), the main canal(s), and more intricate anatomical branches that may connect the root canals to each other or to the surface of the root.
The smaller branches, referred to as accessory canals, are most frequently found near the root end (apex) but may be encountered anywhere along the root length.