Jing (Chinese: 精; pinyin: jīng; Wade–Giles: ching) is the Chinese word for "essence", specifically Kidney essence. Along with qi and shen, it is considered one of the Three Treasures of traditional Chinese medicine.
According to Traditional Chinese Medical theory, jing or essence can be summarised in two parts: the Yin, being congenital or prenatal, and the Yang, being postnatal or acquired. Prenatal jing is acquired at birth from the parents: the father's sperm and the mother's ovum. This is a similar concept to DNA. Postnatal jing is acquired after birth through food, water, oxygen, as well as environmental and social conditions—very much like the concept of epigenetics. The concept is expounded in the Chinese theoretical cosmological treatise called the Bagua and within the I Ching.
The Yin and Yang jing transform to create and replenish each other. The Yang jing circulates through the eight extraordinary vessels and transforms to become and replenish yin; in turn the marrow becomes blood, body fluid and semen. wikipedia 
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