Yes, that's correct! Maria (singular: mare) are large, dark, flat plains on the Moon's surface. They were formed billions of years ago by massive volcanic eruptions that filled ancient impact basins with lava.

Here's a breakdown:

* Flat: Maria are relatively smooth and flat compared to the surrounding, heavily cratered lunar highlands.

* Dark: They appear darker than the highlands because they reflect less sunlight. This is due to their composition, which is primarily basalt, a dark volcanic rock.

So, while the Moon might look like a cratered ball, those dark, flat areas are actually vast plains formed by ancient volcanic activity.