Yin refers to things or substances opposite to yang. It is characterized by quietness, growth, and storage. Yin constitutes tangible substances. Generally, anything that is turbid, substantial, weak, static, descending, or cold is considered as yin. Yin also refers to “yin qi,” one of the two components that constitute the vital qi of the universe or life qi of human being. According to traditional Chinese medicine, yin contains the movement and phenomena in the human body with the attribute of substantial entity, keeping in the interior, concentration, quietness, coolness, moistening, inhibition, and descending.