Jing (精)
Essence — kidney / lower dan tian
Jing (精) — essence; the densest of the three treasures. Stored in the kidneys (which in TCM include the broader pelvic-region 'kidney' system, not only the anatomical organ) and refined within the lower dan tian. Jing has a prenatal component (yuan-jing, inherited at conception, finite) and a postnatal component (replenished from food, breath, and disciplined practice). The Wuzhen Pian frames the first stage of internal alchemy as the gathering and refining of scattered jing within the lower centre — the alchemical phrase 'lian jing hua qi' (refine essence, transform it into qi) names this stage.
Point 1 of 3 in Three Treasures (三寶) — Jing / Qi / Shen
Cross-tradition overlaps
No overlapping points are registered for this point.
Sources
Huangdi Neijing, Suwen (primary_canonical)
Suwen ch. 1 (Shanggu tianzhen lun) and ch. 9 (Liu jie zang xiang lun) treat jing as inherited and cultivated essence and relate it to kidney storage and life development, grounding the medical sense of this treasure.
Zhang Boduan, Wuzhen Pian (primary_canonical)
Wuzhen Pian, poems on the medicine and the first stage of refinement (Pregadio 2009), presents jing as the material gathered and transformed into qi; it supplies the alchemical sense of the lower treasure.