Mare Marginis (Moon)

"Sea of the Edge"

Mare Marginis is a lunar mare that lies on the very edge of the lunar nearside. This mare differs from most of the nearside maria; it has an irregular outline and it appears to be fairly thin. It has small circular and elongated features in the mare plains that probably mark impact craters buried by less than 1000 to 1700 feet of lava. (wikipedia entry)

A mare is a "sea" or large circular plain. On the Moon they are named after latin terms describing weather and other abstract concepts.