The story
central + plain: Calque from Chinese 中原 (Mandarin 中原 (Zhōngyuán),Zhōngyuán; Cantonese 中原 (zung¹ jyun⁴)).
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: The region on the lower reaches of the Yellow River in China which formed the cradle of Chinese civilization. Full definition →