MacWorld has published a nice little tip that allows Lion users to reveal the Dock while in fullscreen apps. To do so, while in any fullscreen app, simply move the pointer all the way to the edge where the Dock is pinned. Once your cursor is resting on that edge of the screen, swipe or move the mouse in that same direction again, as if you were trying to move beyond the edge. The Dock will then spring right up. Pretty cool, huh?
MacWorld also points out that Apple didn't simply go with the "Hide Automatically" Dock feature in fullscreen app mode because many fullscreen apps may have buttons at the bottom or on the sides and automatically displaying the Dock when moving your cursor to the edge of the screen could cause the Dock to block the buttons you are trying to click.
Apple OS X Yosemite