Moon Valley is a term used to describe a type of terrain found on the surface of the moon. It is characterized by long, narrow valleys that are created by the flow of lava. The two crossword solutions for this term are RILLE (5 letters) and RILL (4 letters). Rille is a French word meaning 'GROOVE' or 'CHANNEL', and it is used to describe the long, narrow valleys found on the moon's surface. RILL is a smaller version of a rille, and is usually created by the flow of water. Both rilles and rills are common features of Moon Valley terrain.