Stokes is an impact crater on Mars. It is distinctive for its dark-toned sand dunes, which have been formed by the planet's strong winds. Research released in July 2010 showed that is one of at least nine craters in the northern lowlands that contains hydrated minerals. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On Mars large craters are named after deceased scientists, writers and others who have contributed to the lore of Mars. Small creaters (less than 60km) are named after small towns and villages.