What is a complex crater?

Answer 1

or it could look like a cereal bowl with a hill in the middle

Answer 2

When a really big asteroid hits a planet with a lot of force, the crater explosion forms shockwaves, which causes ripples in the planet, so that when the crater is formed, there are rings, like the expanding rings you see in a pond when you throw something in. Craters with these multiple rings are complex craters. They are most common on the moon, where magma has covered many of them over to form the "seas" of the moon.