, also commonly spelled ch'i, chi or ki, is a fundamental concept of everyday Chinese culture, most often defined as "air" or "breath" (for example, the colloquial Mandarin Chinese term for "weather" is tian qi, or the "breath of heaven") and, by extension, "life force" or "spiritual energy" that is part of everything that exists. References to qi or similar philosophical concepts as a type of metaphysical energy that sustains living beings are used in many belief systems.
Traditional Chinese Medicine applies the philosophies of Yin Yang to treat disease. When the body is in balance between Yin and Yang, health is predominant; when Yin and Yang are imbalanced, disease occurs.