Essence is derived from the innate life substance, a tangible and nutrient substance from parents, and nutrient substances that are acquired later from food and drinks. It is the origin of life and the most basic substance constituting human body and maintaining life activities. Essence could be understood in either a broad or a narrow sense. The former refers to all types of tangible and nutrient substances including blood, body fluids, marrow, and the nutrients from food and drinks, which are believed to constitute human body and maintain life activities. The latter refers to what is stored in the kidney, i.e., kidney essence, including prenatal essence from conception and postnatal essence from food and drinks, which is believed to produce offspring and promote growth and development.