China proper, also called Inner China, are terms used primarily in the Western world in reference to the traditional "core" regions of Chinese civilization centered around the Yellow River and Yangtze River valleys. There is no fixed definition for China proper as many administrative, cultural and territorial shifts have occurred throughout history. One definition refers to the original heartland regions of the Chinese civilization, the Central Plain (southern North China Plain around the lower Yellow River valley) as well as the historical Nine Provinces; another to the Eighteen Provinces inside Shanhai Pass designated by the Qing regime. In contrast, Outer China is a term usually includes the peripheral marchland regions such as Gobi Desert,, Tarim Basin, Northeast China, Dzungaria, Tibetan Plateau and Yungui Plateau, which were historically autonomous regions with unstable allegiance to the authority of Chinese monarchs.
The term was first used by the Europeans during the 17th century to distinguish the historical "Han lands" (Chinese: 漢地, i.e. regions long dominated by the majority Han Chinese population) from "frontier" regions of China where Han populations intermix with other indigenous ethnicities (e.g. Turkic peoples such as Uyghurs, Kazakhs and Uzbeks, Mongolic peoples, and Tibeto-Burmese peoples such as Tibetans, Yi and Bai) and newer foreign immigrants (e.g. Slavic colonists such as Russians and Ukrainian Cossacks), sometimes known as "Outer China". There was no direct translation for "China proper" in the Chinese language at the time due to differences in terminology used by the Qing regime to refer to the regions.