The Libya Montes are a highland terrain on Mars up-lifted by the giant impact that created the Isidis basin to the north. During 1999, this region became one of the top two that were being considered for the canceled Mars Surveyor 2001 Lander. The Isidis basin is very ancient. Thus, the Libya Montes that form the southern Isidis basin rim contain some of the oldest rocks available at the Martian surface, and a landing in this region might potentially provide information about conditions on early Mars. (wikipedia entry)
A mons is a mountain. On Mars they are named after the nearest named albedo feature on the Schiaparelli or Antoniadi maps.