An updated info, an excerpt (copied) from Wikipedia:
Chugoku Region (Chugoku-Chiho), literally means "middle country". In Japanese, the characters 中国 and the reading Chūgoku are also used to mean "China". The same characters are used in Chinese to refer to China, but pronounced Zhōngguó lit. "Middle Kingdom" or "Middle Country".
To avoid confusing "Chūgoku region" with China, the Chūgoku region is also called the "San'in-San'yō region". San'in is the northern part facing the Sea of Japan, which indicates the "shady side of the mountain". San'yō is the southern part facing the Inland Sea, which indicates the "sunny side of the mountain". These names originated from the marked differences inclimate.