The word 精 ching is Chinese, alternately Romanized as jing, tsing, etc), and literally means, "sexual energy, nutritive essence, essence; spirit, sperm, seed; extract; refined, perfected."
Ancient Chinese philosophy says there are three life forces, three "treasures":
These three are mutually interdependent and interconnected.
According to Chinese medicine, ching is the basis of life and health. If there is little ching (life force) then health suffers and life is shortened. This is the basis for sexual continence or retention of the sexual matter. In Taoist alchemy, this understanding is extended by simple logic as the basis for immortality.
"Nothing is more important for the ch'i of man than the ching of the penis." - The Shih wen
"When ching is emitted [through orgasm], the whole body feels weary." - P'eng Tsu, Classic of Su Nu
"If the fuel is exhausted, the flame expires." - Health and Benefits of the Bedchamber
"The essential teaching is to refrain from losing ching, and treasure one's fluids." - P'eng Tsu, Classic of Su Nu
In the most ancient Chinese dictionary, ching is defined as "cleaned rice, seed, source of life." This corresponds to the mystical symbolism in other traditions of rice, wheat, or corn as a reference for the sexual matter.