Die Break. Known as a Cud. Keeper! What happens is that a piece of the Obverse Die breaks away due to deterioration. When it strikes the blank planchet the metal flows into the void. It is never added material as some think.
@bblindt79 There is a website called Cuds on coins See if you can find yours listed http://cuds-on-coins.com/washington-quarter-cuds-no-date-2/
I own a pop machine. I go through a lot of coins. Owned it now for about 3 years and this is the first one like this i have found.