It is a type of large crater (surface depression or pit) left on the surface of a moon or planet, caused by a large object striking its surface. It may include concentric rings or flows of melted rock.
(see also the related link for a video on craters produced in a lab)
Impact Basin / Impact Crater
The Caloris Basin is an impact basin. It is one of the largest impact craters in the solar system. It was created after the heavy bombardment period and is estimated to be 3.8 billion years old.
South Pole-Aitken basin - Moon - Diameter: 2,500 km http://en.wikipedia.org/wiki/Impact_crater#Largest_named_craters_in_the_Solar_System --Geoffrey A. Landis
The usual term is crater. Most craters are nearly circular holes surrounded by rims of ejected material. The term "impact basin" is used for the multiple-ringed structures formed by large impacts.
when meteorites and other objects strike the moon, they leave behind depressions in the moons surface. The depression left behind by an object striking the moon is known as an imoact basin, or impact crater.
Impact crater is now more prevalently used for the term impact basin.
Impact Basin / Impact Crater
South Pole Aitken Basin (diameter 2500km) is not the largest known impact crater. That distinction lies with Utopia Planitia Basin (3500km) on Mars. However, SPA is the deepest known impact basin in the Solar System at 13 kilometers. If proven, the hypothesized Borealis basin, on Mars, would be the largest impact basis, at more than 10000 km in diameter.
A Impact Basin
mascons
The Caloris Basin is an impact basin. It is one of the largest impact craters in the solar system. It was created after the heavy bombardment period and is estimated to be 3.8 billion years old.
True
The South Pole-Aitken basin.
South Pole-Aitken basin - Moon - Diameter: 2,500 km http://en.wikipedia.org/wiki/Impact_crater#Largest_named_craters_in_the_Solar_System --Geoffrey A. Landis
Caloris Basin (also known as the Caloris Planitia) is an impact crater on Mercury about 1,550 km in diameter, known as the largest crater in the Solar System.
The Caloris Basin is a large impact crater found on the planet Mercury, 963 miles in diameter. Its one of the largest craters in the solar system.
The Caloris Basin on Mercury is certainly one of the largest impact craters in the Solar System. As to the largest in the Milky Way - you'll just have to wait and see.