The three treasures, sanbao, in Daoist physiology and inner alchemy are jing, qi and shen: essence, vital energy and spirit. They constitute the person on this account, and their conservation, cultivation and transformation is the substance of internal alchemical practice.
Jing, essence, is the densest of the three: the generative and constitutional substance associated with reproduction, growth and the body's foundational vitality. It is held to be partly inherited at birth and partly acquired from food and air, and to be depletable rather than inexhaustible. A great deal of traditional counsel about moderation, in sexual activity, exertion, sleep and diet, is framed as the conservation of jing.
Qi, vital energy or breath, is the animating movement: what circulates, warms, transforms, holds things in place and defends against intrusion. It is the concept shared most widely across Chinese thought and medicine, and it is the level at which most practice operates, breathing techniques, qigong, taiji, and the therapeutics of acupuncture and herbal medicine are all described as regulating qi.
Shen, spirit, is the most refined: consciousness, awareness, and the presence visible in a person's eyes and bearing. Chinese medicine treats the state of shen as a primary diagnostic sign, and a practitioner is trained to read it directly.
The internal alchemical programme, neidan, is standardly described as a sequence of refinements: refining essence into energy, energy into spirit, and spirit into emptiness, returning to the Dao. That sequence deliberately mirrors the external alchemy, waidan, which it displaced over the Tang and Song, transposing furnace, ingredients and elixir into the body itself. The transposition is one of the major developments in Daoist history and it is what allowed alchemical language to survive the discrediting of alchemical practice.
Two disambiguations are needed, because the same phrase names different things. The Daodejing's chapter 67 also speaks of three treasures, and they are entirely different, compassion, frugality, and not daring to be first in the world. And in religious Daoism a further set of three treasures, the Dao, the scriptures and the masters, functions as an object of refuge, parallel in form to the Buddhist triple gem. The homonymy is a common source of confusion in general accounts.