Tianmian sauce (traditional chinese: 甜麵醬/甜醬; simplified chinese: 甜面酱/甜酱; pinyin: tiánmiànjiàng or tiánjiàng), also known as sweet bean sauce, sweet flour sauce or sweet wheat paste, is a thick, smooth, dark brown or black paste with either a mild, savory or sweet flavor. it is commonly used in northern chinese cuisine, northeastern chinese cuisine, as well as korean-chinese cuisine. peking duck and jajangmyeon are two popular dishes that feature the sauce.
Source: Wikipedia