ALL meanings of mare frigoris
Ma·re Fri·go·ris
M m - noun mare frigoris (Sea of Cold) a dark plain in the northern hemisphere, in the first and second quadrants of the face of the moon: about 55 miles (90 km) wide at its narrowest width and 750 miles (1200 km) long: about 67,000 sq. mi. (174,000 sq. km). 1