Paint correction is the mechanical leveling of clear coat or paint (clear coat is unpigmented paint, clear) to a point where all the paint is free of swirl marks and light scratches.  Swirl marks are essentially a “V” cut/slice in the paint where light bounces around in the valley of the scratch and exits.  This is how you see the swirl marks. If the paint was flat, with no valley, you wouldn’t have anywhere for the light to bounce around…that is where paint correction shines the best.