What is 丑 (chǒu tǔ) in Chinese metaphysics?

Yin Earth of the northeast (Gen palace), commanding late winter; hides Ji, Gui and Xin — the tomb-storehouse of Metal, cold damp soil.

Original (Chinese): 东北艮宫阴土，居腊冬之令，藏己癸辛，为金之墓库与湿润寒土。