What you are seeing is the result of a badly worn die. Over time as many coins are struck the dies begin to deteriorate. The dies can become misshaped, loose metal, become deformed among many other issues. This is not a collectable or recognized error or variety. Some coins with certain varieties or more serious issues like die cracks, doubled dies and off-center strikes etc. are more sought after and some highly collectable. What the coin you have posted shows is die deterioration and deformation causing portions of the coins devices in the lettering to be unstruck or miss struck. This type of condition on a coin is a very common quality control issue from the US Mint which effects millions of coins. It is not considered an error it is just the result of bad quality control and trying to squeeze every penny out of the US Mints coin dies.