The lunar maria (singular: mare) are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruption. They were dubbed "maria" (Latin for "seas") by early astronomers who mistook them for actual seas.
They are less reflective than the "highlands" as a result of their iron-rich compositions, and hence appear dark to the naked eye. The maria cover about 16% of the lunar surface, mostly on the near-side visible from Earth. The few maria on the far-side are much smaller, residing mostly in very large craters.
The traditional nomenclature for the Moon also includes one oceanus (ocean), as well as features with the names lacus (lake), palus (marsh), and sinus (bay). The latter three are smaller than maria, but have the same nature and characteristics.
Lunar anorthosites constitute the light-coloured areas of the Moon's surface and have been the subject of much research. Template:Terrains