山区(shān qū) - mountain area, mountainous region in Mandarin

山区 (shānqū) is a mountainous area or region. 山 (shān) means "mountain, hill" and 区 (qū) means "area, district, zone", the same 区 you get in 市区 (shìqū), "urban area", and 郊区 (jiāoqū), "suburbs".

It is used geographically rather than for a single peak, so it describes a whole tract of hilly, mountainous terrain: 生活在山区 (shēnghuó zài shānqū), "living in a mountain area", 山区的天气 (shānqū de tiānqì), "weather in mountain areas", both common in descriptions of remote or rural China.

山区 often pairs with 农村 (nóngcūn), "countryside", since many mountain areas are also rural, but the two words are not synonyms: 农村 is about farming and village life, while 山区 is purely about the terrain, and a place can be flat countryside without being 山区 at all.