Laozi's Classic of Tao Te Ching and the simple Classic of Three Characters. The reason why it is called Neijing is not that "five yin and one yang are called Neijing" as Wu Kun's Su Wen Zhu and Wang Jiu's Neijing Economic Cooperation said.
It's not what Zhang Jiebin said in The Analects of Confucius that "the inside is the Tao", but the opposite of "the outside". This is similar to Hanshu, Hanshu, Chunqiu, Chunqiu, Zhuangzi's Inner Chapter, Han Feizi's Hidden Inside and Waizang, except that Huangdi Waijing and Bai's classics have been lost. ?
The origin of the name
Ji Fanglue, a chronicle of Han Shu's literature and art, contains four Chinese medical classics: Medical Classic, Classic Prescription, Immortal and Room, among which Huangdi Neijing is included in Medical Classic.
The so-called "medical classics" is a book that expounds medical theories such as human physiology, pathology, diagnosis, treatment and prevention. It is called "Beijing" because of its importance. The ancients generally called important books with certain rules that must be studied "classics", such as the Confucian "Six Classics".