氣

Qi 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, especially in Asia. 

Philosophical conceptions of Qi date from the earliest recorded times in Chinese thinking. One of the important early figures in Chinese mythology is Huang Di or the Yellow Emperor. He is often considered a culture hero who collected and formalized much of what subsequently became known as traditional Chinese medicine. Although the concept of Qi has been very important within all Chinese philosophies, their descriptions of Qi have been varied and conflicting. 

The etymological meaning of the Qi ideogram in its traditional form 氣 is "气 steam rising from 米 rice as it cooks" (source: Wenlin dictionary), which could be interpreted as the indicating the link between matter and the energy it develops. Matter and energy are said merely to be different states of the same fundamental substance.  One significant difference has been the question of whether Qi exists as a force separate from matter, if Qi arises from matter, or if matter arises from Qi. Some Buddhists and Taoists have tended toward the second belief, with some Buddhists in particular tending to believe that matter is an illusion. 

By contrast, the Neo-Confucians criticized the notion that Qi exists separate from matter, and viewed Qi as arising from the properties of matter. Most of the theories of Qi as a metaphor for the fundamental physical properties of the universe that we are familiar with today were systematized and promulgated in the last thousand years or so by the Neo-Confucians. Knowledge of the theories they espoused was eventually required by subsequent Chinese dynasties to pass their civil service examinations.