The way that the ancient Chinese Taoist(ACT) in describing the definition of Neidan is very esoteric and fictional. For the relevancy of the thread, I will try to be simple, brief and nonfictional.
內丹氣功(Nei Dan Chi Kung)
(1) What is the Neidan method?
Using the alchemical theory to describe the Neidan method, it is a form of Chi Kung
The Naidan method is Chi Kung with the description of alchemical theory. Neidan is categorized as Chi Kung but it is a different concept of Chi Kung. Chi Kung was way before the Neidan method. There were many talks about Chi Kung during the Warring States. Until the East Han Dynasty, people were begin to talk the Neidan Chi Kung.
Neiddan was came very late after the Waidan Method. The ACT try to find immortals and hunted for elixir but failed. Thus they tried to make the own elixir and alchemical pills but they have no effect. Thus they came up with a alchemy theory for internal elixir(Neidan) -- Chi Kung.
The Neidan Chi Kung is only an offshoot of Chi Kung. It even includes more features, such as still sitting, indexing, hard Chi Kung and 辟穀(unknown) etc. The Neidan method belongs to the Chi Kung System of the Taoist religion. The Neidan method is practiced by Taoists; and Chi Kung is universal. However, the most scholars practice Chi Kung. unfortunately, the brief description of Neidan was kind of ridiculous and farfetched. Hence, nowadays, there are not many people are willing to accept it.
Ref:Neidan Chin Kung(內丹氣功)
Using the alchemical theory to describe the Neidan method, it is a form of Chi Kung
The Naidan method is Chi Kung with the description of alchemical theory. Neidan is categorized as Chi Kung but it is a different concept of Chi Kung. Chi Kung was way before the Neidan method. There were many talks about Chi Kung during the Warring States. Until the East Han Dynasty, people were begin to talk the Neidan Chi Kung.
Neiddan was came very late after the Waidan Method. The ACT try to find immortals and hunted for elixir but failed. Thus they tried to make the own elixir and alchemical pills but they have no effect. Thus they came up with a alchemy theory for internal elixir(Neidan) -- Chi Kung.
The Neidan Chi Kung is only an offshoot of Chi Kung. It even includes more features, such as still sitting, indexing, hard Chi Kung and 辟穀(unknown) etc. The Neidan method belongs to the Chi Kung System of the Taoist religion. The Neidan method is practiced by Taoists; and Chi Kung is universal. However, the most scholars practice Chi Kung. unfortunately, the brief description of Neidan was kind of ridiculous and farfetched. Hence, nowadays, there are not many people are willing to accept it.
Ref:Neidan Chin Kung(內丹氣功)