Herschel is a 304 kilometer Impact Basin in the Martian southern hemisphere, at 14.5°S, 130°E, located in the Mare Tyrrhenum region of Mars. (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.