Metal piece on blackberry playbook?

I received a BlackBerry Playbook as a gift, it has this round thing on the back of it that actually makes it easy to hold. I'm just wondering what it is because it seems attached but I don't see it on any of the other ones. Any help would be appreciated, thanks!

The back of a playbook is smooth. Whatever it is, we can't guess, since we do not have clairvoyant powers.

You could post a screenshot or ask the nice person that gifter you the tablet.