The first image below shows the relationship among three craters that are near each other. Keeler Crater is to the North Crater. After Keeler was formed, a later impact formed Trumpler Crater, and in the process destroyed part of Keeler. (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.