山芋 is a term for an edible tuber, but it can refer to different plants depending on region and context. In northern China it often means 'sweet potato' (like 红薯 or 地瓜), while in some other areas it can refer to the Chinese yam (山药, Dioscorea polystachya). When you see this word in a menu or grocery, you'll need to check local usage — it's not interchangeable with the scientific English terms 'yam' and 'sweet potato'. The word is more common in certain dialects than in standard Mandarin.