What is a crater on a planet or moon?

Impact craters are among the most common surface features in the Solar System. They form when a fast-moving object strikes a surface and excavates material, leaving a circular or oval cavity. Airless bodies like the Moon preserve craters for billions of years because they have little erosion or plate tectonics. On Earth, weather, water, and geology erase many old craters, so only the most recent or largest remain visible.