Neidan, inner alchemy, uses the language of laboratory alchemy for meditation and breath practices within the body. Essence is refined into energy, energy into spirit, and spirit returned to emptiness, forming the golden elixir. It flourished from the Song dynasty, especially in the Quanzhen school.
Neidan
Inner alchemy: Daoist practices that refine the body’s vital energies into an immortal spirit.
Also: internal alchemy