That would be Die Deterioration. As the dies age and produce coins, parts of the die start to show this. And deterioration tends to get stronger towards the rims.
It also looks like your coin has die flow lines in the field behind Lincoln's head. Produced with age as the metal continually flows across the surface of the die. An analogy might be to compare these to streams/rivers being cut into the ground from water flowing across the surface. The more water that flows through a stream over time the deeper they become.