2015 D Shield Penny. Error Or PMD?

Looks like a coin scratch. Note how the 'N' is reduced in size compared with the other
N' on cent?

Errors or varieties? There have been a few nice DDR's. But they are mostly found in the Philly cent areas. Here is Denver land, not much going on so far.

It's a PMD.it's the kind of scratch I often see from coin rolling machines.

PSD (Post-Strike-Damage) is usually incuse. Contact with another coin, alteration of a coin, coin scratch from handling are all damage. Not an error. Imagine getting a new car and smacking it on the fender with a sledgehammer. That is damage. It wasn't an error from the factory. It was an event that altered your car. Lowers the value as the car now sits. There are other events that cause an incuse mark on a coin. Struck through wire/grease/debris/oil/rust on the die and other events. These usually alter the value by the damage they create. But a struck through wire/staples/other things struck on to the coin will raise the value. But most of the time the coin was damage after the coin was struck. These are called circulation damage. The OP's coin may have been struck through a small thin wire or just a coin scratch. How to tell the difference? A struck through wire will leave a rounded area on the bottom of the trench caused by the wire/fiber/thread.

On a coin scratch, they are usually squared in shape.

Depending on what caused the scratch.