Edge Lighting is a backlight system where LEDs are placed only along the edges of the TV screen.
The light then spreads across the panel to brighten the whole display. This design makes TVs slimmer and cheaper, but contrast and black levels are usually weaker than Full Array or OLED TVs.
For example, in a dark movie scene, the black areas may look a bit gray because the light is coming from the edges instead of being controlled in small zones.
See also: Backlight, Full Array Local Dimming (FALD), OLED, Contrast Ratio.