That is considered a "cud" error. Thats when a piece of extra metal is left behind in minting, then transfered to the next coin. The value of it is minimal, it is a clloectable tho. If it came up at auction (do I sound like the Antique Roadshow?) say it would maybe bring a couple of bucks. Hope that helps.
However, the reason for the error is that a (usually) small part of the die has broken off, from the edge. As a result, the coin struck will not show the detail from the part of the die that is missing.
If you see a die break from one edge to another that is the start of a die's failure, usually due to excessive wear.
In this instance, the 'cud' is nice and larger than normal. Very collectible.