As already mentioned,
Die Deterioration. As the die wears on the single squeeze dies, the wear appears beyond the device, but on the field area.

We often see this on the obverse side of cents:

How to identify it? It always flows towards the closest rim direction. Like on the coin above the date shows on the right side, LIBERTY shows on the left side and on the motto, it is on the tops of the devices as that is the direction of closest rim. No premium for these.