Show the Dock in Full Screen Apps in Mac OS X
The Dock disappears whenever an app is put into Mac OS X full screen mode, but that doesn’t mean you can’t access the Dock if you need it. To show the Dock in a full screen app, swipe twice at the bottom of the screen, the first swipe won’t show anything but the second swipe will draw the Dock upwards as usual.
Regardless of Dock auto-hide settings this will activate the same way so long as the user is in full-screen mode for any given app. This is the only way to reveal the Dock under such circumstances, and the feature is defaulted this way because it reduces screen clutter and maximizes the on-display room for the given app. On a huge display like an iMac that may not seem to meaningful, but on smaller screened Macs like the MacBook Air, this makes a lot of sense and is very useful.
This feature is exclusive to versions of OS X that have full screen app mode, which was introduced in OS X 10.7 and continues in OS X 10.8 Mountain Lion, OS X 10.9 Mavericks, and presumably into the future.