A fundamental difference between Eastern and Western medicine is that many of the Eastern traditions include practices that help one to develop and achieve optimal health and wellness before the onset of disease, infection and emotional problems. Prescribing Qi Gong to prevent and cure illnesses of the body, mind and spirit is quite typical for Chinese medicine practitioners, but anything similar is almost unheard of in Western healthcare.
In Chinese medicine and philosophy, Qi is thought of as “the natural force which fills the universe,” and while there are many ways of defining Qi, it may be generally thought of as any and all types of energy which are “able to demonstrate power and strength,” including the power to animate objects with life. 
“It is known that all diseases arise from the upset of qi: Anger pushes the qi up, joy makes the qi slacken, grief disperses the qi, fear brings the qi down, terror confuses the qi, and anxiety causes the qi to stagnate. Anger harms the liver, joy the heart, anxiety the spleen, grief the lungs, and fear the kidneys.” – The Nei Jing
Primarily handed down from generation to generation by word of mouth and in actual practice, not in written texts, the ancient Chinese practices of Qi Gong can vary wildly between teachers and schools of thought. It can be many things including physical exercises (both standing and seated), forms that resemble martial arts, breathing exercises, visualizations and, or, meditations.
The system is incredibly diverse, however, the science behind the flow of energy in and around the body has been well documented for thousands of years, and many schools of thought are in concurrence about many of the basic and even more esoteric concepts and terms involved. Among the most important concepts in Qi Gong training is an understanding of what are known as ‘San Bǎo’ (三寶), or, The Three Treasures.
Jing (Essence), Qi (Internal Energy), and Shen (Spirit), are the Three Treasures, The Three Foundations, or The Three Origins, and are the root of life.
“In Qi Gong training, a practitioner learns how to ‘firm his jing,’ and how to convert it into Qi. This is called ‘Lian Jing Hua Qi,’ which means to ‘to refine the Jing and convert it into Qi.’ Then he learns how to lead the Qi to the head to onvert it into Shen. This is called ‘Lian Qi Hua Shen,’ which means ‘to refine the Qi and convert it into (nourish) the Shen.’ Finally the practitioner learns to use his energized Shen to govern the emotional part of his personality. This is called, ‘Lian Shen Liao Xing, or ‘to refine the Shen to end human (emotional) nature.’” -Dr. Yang, Jwing-Ming 
Jing means a number of things and as a word it can be used as a noun, a verb or an adjective. It is considered the essence, the original source from which a thing is made, and also the refining process by which a person’s essence is polished or sharpened. Jing is the energy given to you at birth that enables you to grow and to develop strength. Many believe it to be the most important part of a you because it is considered to be the root energy to Qi and Shen. Learning first how to conserve and firm your original Jing is critical to Qi Gong training.
Qi is, again, the energy that fills the universe. There really is no clear explanation of how it works or of the vessels ….
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Source: transients.info: The Three Taoist Treasures of the Energy Body