China Proper
China proper, Inner China or the Eighteen Provinces was a term used by Western writers on the Manchu Qing dynasty to express a distinction between the core and frontier regions of 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 North China Plain; another to the "Eighteen Provinces" system of the Qing dynasty. There is no direct translation for "China proper" in the Chinese language due to differences in terminology used by the Qing to refer to the regions and the expression is controversial among scholars, particularly in China, partly because it implies the frontier regions outside China proper are in some way separate or even illegitimate territories of China.
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 China's 18-provinces from its newly acquired properties. 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. When describing the Chinese Empire under the Qing dynasty, Winterbotham divided it into three parts: China proper, Chinese Tartary, and the States Tributary to China. He adopted the opinions of Du Halde and Grosier and suspected that the name of "China" came from Qin dynasty. He then said: "China, properly so called,... comprehends from north to south eighteen degrees; its extent from east to west being somewhat less..."
...
Wikipedia