The vital life force in the body, supposedly able to be regulated by acupuncture. It corresponds roughly to the Greek pneuma, the Latin spiritus, and the ancient Indian prana. The concept of life-breath or vital energy was formulated as an indication of the awareness of man, originally directed externally toward nature or society but later turned inward to the self or life within. (From Comparison between Concepts of Life-Breath in East and West, 15th International Symposium on the Comparative History of Medicine - East and West, August 26-September 3, 1990, Shizuoka, Japan, pp. ix-x)

百度先生翻译参考：体内重要的生命力,被认为能由针灸调节。大体上与希腊精神,拉丁圣灵,古印度prana。生活气息的概念或生命力作为人类意识的表示,制定最初向自然或社会外部但后来闭关自守自我或生活中。(东方和西方的生活气息比较概念,比较历史国际研讨会）

中医药学主题词表的定义：

人体及维持生命活动的最根本、最微细的物质，同时也具有生理机能的含义。在中医学术语中，气与不同的词合用表达各种不同的意义。