I think you're asking about the moon's "mares," which are broad, relatively smooth plains on the lunar surface. The word "mare" is Latin for sea, which is what early astronomers mistook the plains for.
Maria
The craters on the Moon's maria can vary in size, but some can be several kilometers in diameter. The largest known crater on a lunar mare is the Orientale Basin, which is about 930 kilometers in diameter.
Without a telescope, you can see the different phases of the moon, lunar craters, and dark patches known as lunar seas or maria. You may also see some of the moon's prominent features, such as the Tycho crater or the Apennine Mountains.
Saturn's moon with the crater Herschel is called Mimas. Mimas is one of Saturn's innermost moons and is known for its large Herschel crater, which gives it a distinctive "Death Star" appearance.
mountainous crater regions and the light colored ray systems of a few impact craters
The South Pole-Aitken basin (not "Aitken crater") on the far side of the moon, at 1,600 miles across, is not only the largest known impact crater on the moon but one of the largest in the solar system. It is also believed to be the moon's oldest and deepest (over 8 miles deep).
This is known as an impact crater. Please see the related link.
There is a "Herschel Crater" on our own Moon; on Mimas; and on the planet Mars.
The large flat areas on the moon are called "Maria" (Latin for "seas", because the early astronomers thought that's what they are). They are huge regions of smooth rock. If very dark, they are so by being in shadows. Smaller dark spots are meteor-impact crater floors in the shadows of the crater wall.
The cheese crater. The cheese crater is the cheeseiest crater in all of cheese land.
Lunar craters are found on the surface of the Moon. They are formed by impacts from meteoroids, asteroids, or comets hitting the Moon's surface. Some well-known lunar craters include Tycho, Copernicus, and Aristarchus.
The astronauts explored the giant crater left by the meteor impact.