Huygens is an impact crater on Mars named in honour of the Dutch astronomer, mathematician and physicist Christiaan Huygens. The crater is approximately 456 km in diameter and can be found at 304.4°W 14.0°S, in the Iapygia quadrangle. Scientists were delighted to see branched channels in pictures taken with spacecraft that were sent in orbit around Mars. The existence of these channels is strong evidence that much water once flowed on the surface of the planet. (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.