Gravity Well

The area of space around a celestial body that is dominated by the body's gravitational field.

The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites.[not verified in body] It is sometimes termed the Roche sphere. It was defined by the American astronomer George William Hill, based on the work of the French astronomer Edouard Roche. https://en.wikipedia.org/wiki/Hill_sphere