LED stands for light-emitting diode. LEDs are similar to very small lights that illuminate when electric current goes through the diode.
 LED display
An LED display is often just called an LED TV or LED monitor. In these cases the display screen is still the same as an LCD screen but the difference is the underlying backlight is created using LEDs as a light source.
 Enhanced contrast
In portable devices the LED lighting in an LCD display is done with light guides using a few LEDs along the edge of the screen. Larger LCD displays have a rectangular array of LEDs directly behind the screen. With a large amount of LED devices a uniform white background can be obtained. However it is possible to treat the array of LEDs as a display medium just like the screen itself. By controlling areas of the back screen independently it is possible to enhance the contrast of the display. Say, for example, a portion of the screen image is supposed to be very dark, it can be made even darker by turning off the LED lights in back of that area. It is possible to treat the layer of LEDs as if they were a lower resolution black and white screen behind the LCD screen and sending the same signal to both screens which would be have more contrast than would be available if the LCD back screen was lit uniformly.
 Direct LED display
It is possible to use LEDs as both the light source and the actual data display itself simply by making an array tiny LEDs. This is also done with OLED displays and QD-LED displays which are specialized extensions to standard LEDs.
 Backlight vs. Frontlight
The goal of a backlight and a frontlight is basically the same: To illuminate the screen so that it can be viewed in the dark. The use of the correct lighting is determined by the way a particular screen works. Often people use the term backlight when the really mean just some sort of illumination without regard to whether it is in back or in front of the screen but this can be confusing to those who know the difference. A Backlight provides illumination behind the screen. In a mobile device this is actually done by placing the LED lights along the edge and then using a light guide to direct the light itself to light up the full back of the screen. An LED frontlight is done almost the same way. The LED lights are also placed along the edge of the display and there is also a light guide to distribute the light over the full screen. The difference is that the lightguide in this case is in front (on top of) the screen and is therefore transparent so you can still view the data underneath. The two light methods are not in competition as generally speaking only one of them will work depending on the type of screen you have. If you need a general term it can be called an edge light.