It is die wear. On the older process of making dies (I call them Multi-hubbed dies) the die wear starts to breakdown on the sides that face the rim. The edge of the devices loose their shape first. Then the curve goes away and eventually devices start start flowing towards the rims.

If the earliest die states that edge near the rim is strong and sharp. After a few thousand coins, this edge (closest to the rim on the die) goes away and we see it start to break down like the image I posted above. I call this die wear. The devices on these coins and the designs are what I call as high profile devices. The wear starts on the tops of these devices and eventually affects the lower part of the devices.
This is different from
Die Deterioration in the way it happens. On the lower profile dies (single squeeze dies, the devices are not as tall and they start to show deterioration
next to the devices not on the devices like you would see on die wear.

Note how the fields are affected, rather than the devices like on the previous die wear devices as mentioned above. Thus I call the example form
Die Deterioration on examples of the single squeezed dies as that deterioration as it affects not the devices, but the fields next to the devices. On this example, post above, the date shows on the right side of the coin, the LIBERTY to the left side of the coin and on the motto, the tops of the devices. Just like die wear they follow the same direction, but affect the die in a different area. So I call them as I see them. If they affect the devices themselves I call them die wear. If they affect the area next to the devices on the fields, I call them
Die Deterioration. True both are die wear, but how the way is different.