Zunil is an impact crater near the Cerberus Fossae on Mars, with a diameter of 10.4 km Visible in images from the Viking 1 and Viking 2 Mars orbiters in the 1970s, Zunil was subsequently imaged at higher resolution for the first time by the Mars Global Surveyor in 2000. A ray system associated with the Zunil impact, visible in infrared images from the Mars Odyssey Thermal Emission Spectrometer was later detailed by McEwen et al. (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.