The term 'Lunar Region' refers to the surface of the moon. It is composed of two parts: seas and mares. A SEA is a large body of water, usually salty, that covers much of the Earth's surface. On the moon, seas are dark, flat areas that were created by ancient lava flows. MARE is Latin for 'SEA' and is used to describe the large, dark patches on the moon's surface. These patches are made up of basaltic rock that was formed from ancient volcanic eruptions.