A diode is an electronic component with two terminals. The main function of the diode is to allow current to flow in one direction, but not in the opposite direction.
LEDsLight emitting diode
LEDs give light when a current flows through the diode. LEDs are used in many electronic devices as indicators.
Zener diodeZener diode
A zener diode also allows the current to flow in the opposite direction when the zener voltage is reached. Zener diodes are used to supply reference voltages and to prevent overvoltage.