LED stands for "Light Emitting Diode."
These are tiny light bulbs that don't have a filament that will burn out like traditional incandescent light bulbs, nor do they get very hot. They are illuminated solely by the movement of electrons in a semiconductor material.
LEDs can last up to 60,000 hours, compared to less than 1,000 hours for incandescent bulbs. LEDs common in exit signs, stoplights, and some holiday lights.