1) Type of lamp 
A backlight is a form of illumination used in liquid crystal displays (LCDs). As LCDs do not produce light themselves (unlike for example Cathode ray tube (CRT) displays), they need illumination (ambient light or a special light source) to produce a visible image. Backlights illuminate the LCD from the side or back of the display panel, unlike fro...
(from the article `liquid crystal display`) The backlight of LCDs typically accounts for more than 80 percent of the display`s power consumption. For mobile complex displays, battery lifetime ...
A light which is generally mounted behind a subject to light the subject's hair and shoulders without illuminating a subject's front. (Lighting)
A built-in light source transmitted from the rear of the display, to allow them to be read.
The rear glass window glass.
The purpose of a backlight is to create a sculpted dimension behind a prop or performer to set them apart from the background. You can adjust your backlight’s angle and intensity to be very noticeable or have a more subtle halo effect. You can also use a backlight to establish a sense of depth on a set.
The illumination for a colour LCD display on digital cameras or phones.
Pump screen light. Turns on whenever the button is pressed or in combination with the button if not on the HOME screen. The backlight also appears during alarms and alerts, except for LOW BATTERY alert and OFF NO POWER alarm.