The China proper (中國本土), Inner China (中國內地) or Eighteen Provinces inside the Pass (關內十八省) is a term used by some Western writers in reference to the traditional "core" regions of China.
This term was first used by Westerners during the Manchu-led Qing dynasty to describe the distinction between the historical "Han lands" (漢地) — i.e. regions long dominated by the majority Han population — and the "frontier" regions of China where more non-Han minorities and new foreign immigrants (e.g. Russians) reside, sometimes known as "Outer China". There is no fixed extent for China proper, as many administrative, cultural, and linguistic shifts have occurred in Chinese history. One definition refers to the original area of Chinese civilization, the Central Plain (in the North China Plain); another to the Eighteen Provinces of the Qing dynasty. There was no direct translation for "China proper" in the Chinese language at the time due to differences in terminology used by the Qing to refer to the regions. Even to today, the expression is controversial among scholars, particularly in Mainland China, due to issues pertaining to contemporary territorial claim and ethnic politics.
Outer China usually includes the geographical regions of Dzungaria, Tarim Basin, Gobi Desert, Tibetan Plateau, Yunnan–Guizhou Plateau, and Manchuria.
It is not clear when the concept of "China proper" in the Western world appeared. However, it is plausible that historians during the age of empires and the fast-changing borders in the eighteenth century, applied it to distinguish the 18 provinces in China's interior from its frontier territories. This would also apply to Great Britain proper versus the British Empire, which would encompass vast lands overseas. The same would apply to France proper in contrast to the French Empire of the time, which Napoleon managed to expand all the way to Moscow.
According to Harry Harding, the concept can date back to 1827. But as early as in 1795, William Winterbotham adopted this concept in his book.