Not an error. It has been grinded down purposely. It's Post Strike Damage (meaning that it happened after it left the U.S. Mint), and it's only worth face value (5 cents).
Errers and Varietys.
More information about Die Deterioration? http://goccf.com/t/317950
Retired U.S. Mint Coin Die Set information. http://goccf.com/t/302961
1988 P LMC
RDV-006, 1998 P LMC
Wide AM, and 2000 P LMC
Wide AM. http://goccf.com/t/327834 http://goccf.com/t/294303 http://goccf.com/t/312900
1973 D Lincoln Memorial cent
With Recurring Die Subsidence Error Information. http://goccf.com/t/304624 Machine Doubling
Die states progression on coins. Scroll down, so you can see the different die state progressions. http://goccf.com/t/325638