It's either a die crack or a die gouge (or scratch). I vote for die gouge (or scratch). Die cracks are usually very jagged and yours is fairly straight.
I will be the first one to admit that I am far from being an expert on coins and errors. But wouldn't a gouge remove metal from the coin? The pic seems to show a buildup of metal above the surface.
Definition: A die crack is a mark appearing on a coin, usually in the form of a fine raised line or small blob. This happens because the coin die which struck the coin had a crack or small break in it that got transferred to the planchet during striking. Although most die cracks are considered a defect, some of them are collectable, such as the spiked head type. Cheryl
I have seen a lot of these on the zinc cents, and sometimes it is air that gets trapped between the zinc core and copper outer shell. At one point I wanted to test my theory and used a strong wooden tooth pick to rub on the area and it actually flattened out. jeankay
Ive never heard about a Die Gouge before, But that does seem like a correct assessment. It doesn't look like a Die Crack. If there was a Die Gouge wouldn't it be recognized, thats pretty serious... and noticeable
It could be that a few coins produced by the die after it got scratched or gouged fell into the hopper along with coins produced before the gouge/scratch. When the press operator inspected a sample coin from the hopper he happened to pick one produced before the die was damaged and released all the coins in the hopper - including those with the die gouge/scratch marks. The next time the press operator checked the coins in the hopper he most likely noticed the die gouge/scratch and culled the coins in the hopper and replaced the damaged die. But by then those few coins with the gouge/scratch had already made it past inspection.
So how would a die gouge happen? By a clash with another die? But that would be a "die clash" and would most likely show an image, right?
One way a die gouge can occur is when the feeder finger does not retract and is struck by the hammer (upper) die.