It means the light source is in front of the screen [1]. There is a transparent light guide covering the screen. The lighting comes from 4 LEDs at the bottom edge of the screen, and enters the light guide. It exits the bottom of the light guide all over the area of the screen, reflects off the screen, passes through the transparent light guide, and out to your eyes.
[1] http://www.nytimes.com/interactive/2012/12/26/technology/lig...