Mare

Plural  Maria,   any flat, dark plain of lower elevation on the Moon. The term, which in Latin means “sea,” was erroneously applied to such a feature of the lunar surface by telescopic observers of the 17th century. In actuality, maria are huge lava flows marked by ridges, graben, rilles, and faults and are devoid of any water. There are 14 surficial areas of this type, and all of them occur on the side