With the traditional LCD, the bulky display cell of the LCD is backlit with a line of lights or a single lighted panel. With LED, the LCD cell and assembly is still backlit but with individual lights, making up a large grid of individual lights.
What makes OLED displays better is the infinite contrast and true black. Long gone are the days of a white wash effect that turns dark bold colors into lighter colors because of white backlighting. Now all colors are projected as their true color, not just lit up with white lighting.