China proper, Inner China or the Eighteen Provinces was a term used by Western writers on the 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.