Clicking it will show your dashboard in full screen. In the upper right corner are full-screen controls that allow you to rotate the dashboard or exit full-screen mode.
After a few seconds of not wiggling your mouse, the full-screen controls will slide out. Just wiggle your mouse to bring them back.
If you want to remove the full-screen controls all together, or allow the dashboard to be embedded in another website (using an IFRAME), you can manually change the dashboard's URL from something like: