Montes Apenninus are a rugged mountain range on the northern part 's near side. This range forms the southeastern border of the large Mare Imbrium lunar mare and the northwestern border of the Terra Nivium highland region. It begins just to the west of the prominent crater Eratosthenes, which abuts against the southern face of the range. (wikipedia entry)
A mons is a mountain. On the Moon they are named after terrestrial mountain ranges, nearby craters, and deceased scientists who have made outstanding or fundamental contributions to their fields.