[1] Porkert describes the concept as "the metaphorical designation of the inborn constitution, the vital potential that is gradually used up in the course of life.
The term has been used since at least the Han dynasty, where it is found in the chapter 'Lu Li Zhi Shang/律历志上' of the History Book, 'Han Shu.
'[2] In modern times it has come to be used in a colloquial manner in Japanese (where it is pronounced genki (元気)) to mean "healthy" or "energetic", a usage that has more recently been borrowed back into Chinese.
This colloquial usage of the term forms the basis of a variety of Japanese expressions, including the standard casual greeting, genki desu ka (元気ですか), which translates to "are you well?".
in English, it is a rhetorical question and generally answered in the affirmative.