Plato is a "flooded" crater that filled with lava after it was created by an impact. A large one. It's floor is relatively flat and largely unscarred (save for a few small craters). A link can be found below for more information.
The main crater is Caloris Basin.
volcanic
Borealis Basin is significantly larger than Hellas Crater. Borealis Basin, located in the northern hemisphere of Mars, spans approximately 8,500 kilometers (5,300 miles) in diameter, making it one of the largest impact features in the solar system. In contrast, Hellas Crater, situated in the southern hemisphere, has a diameter of about 2,300 kilometers (1,400 miles). Therefore, Borealis Basin is much larger than Hellas Crater.
Impact crater is now more prevalently used for the term impact basin.
The basin shaped crater at the top of a mountain is called a caldera. It forms when a volcano collapses into itself after an eruption, creating a large, circular depression.
The basin-shaped crater at the top of a volcano is called a caldera. It is typically formed after a volcanic eruption causes the volcano to collapse inward, creating a large depression. Calderas can range in size from a few kilometers to tens of kilometers in diameter.
A circular basin surrounded by mountains is typically referred to as a crater or caldera, depending on whether it was formed by volcanic activity or by the collapse of a volcanic cone.
Caloris Basin I think is the deepest and the youngest too.
Recessed area like a crater that is not too deep
Calderas, like Crater Lake, Oregan, USA.
There are no craters on Neptune because its made almost entirely of gases.
The largest known impact crater in the universe is the South Pole-Aitken basin on the far side of the Moon. It measures about 2,500 kilometers in diameter and is one of the largest, deepest, and oldest impact craters in the solar system.