The term 'Lunar Seas' refers to the dark, flat areas on the surface of the moon that are composed of basaltic lava. The most well-known of these seas is the Mare Imbrium, which is Latin for 'Sea of Rains'. The other lunar seas include the Mare Serenitatis, Mare Tranquillitatis, Mare Crisium, and Mare Nectaris. The crossword solution for this term is MARIA, which stands for 'Moon and Related Features Identified from Apollo'. This acronym was coined by the Apollo astronauts to refer to the various features they observed on the moon's surface.