That is a Die Break mint error. The Die that was used to strike the Blank had that area break off. Did you find it? It's called a CUD. Nice finds! Check out this website - http://cuds-on-coins.com
Nice CUD as everyone has said. Here is the no date Cuds on file. See if you can match it up. It looks like a Zinc cent (REV steps and pillars) http://cuds-on-coins.com/lincoln-cent-cuds-no-date/ If you don't find an exact match it could be a later or earlier die state. @paddyman98 does it look zinc to you?
I didn't see that. @ken454 #20 is copper. I believe the (ZN) refers to it being zinc. #22 looks like it could be it also. But if we look at the area opposite cud (rev) it looks more like #20. I am just wondering if that is actually used in the diagnosis. I am thinking a different die state than what is shown on Cuds on Coins. Clearer photos would help. @mikediamond @Conder101
It's that and what looks like zinc also on the reverse. It is best if you attach the photos like you originally did, Make them clear (stabilize your camera) Crop out everything but the coin and post in full size, (not thumbs)
A cud is part of the die (making the coin) has broken away leaving the "blob" look at the rim area of a coin. Really nice find fella, you are very lucky.
I only have a scale accurate to whole grams. I weighed this coin and 9 other zinc ones and all weighed 2. Weighed 10 copper pennies and all weighed 3. Here are some full size cropped pics, best I can do at the moment:
