I didn’t get one of these but my friend Joel was nice enough to share his screen shot.
If you have purchased books from Apple (even e-books) in the last little bit you may have one of these in your inbox. Basically the lawsuit alleged (and judging by this proved) that Apple and Amazon were violating prices set by the publishers for new release books. If you want to see what it was all about you can spend some time on Wikipedia.
Log into your account to check to see if you have any credits in your account. They would have been automatically added and will come off your next purchase like a gift card at checkout.