Neidan , a method of internal alchemy. Part of the Chinese alchemical meditative tradition that is said to have been separated into internal and external at some point during the Tang dynasty.
The neidan tradition of internal alchemy was practised by working with the energies that were already present in the human body, as opposed to using natural substances, medicines or elixirs, from outside of the body. The Shangqing tradition of Daoism played an important role in the emergence of neidan alchemy, after using Wiedan mainly as a meditative practise, and therefore turning it from an external to an internal art.
Closely related to Daoism, it is believed that the goal of neidan was to merge the two energies of yin and yang, and return to the primordial unity of the Dao.