A diode is a two-terminal electronic component that conducts current primarily in one direction; it has low resistance in one direction, and high resistance in the other.
Use of diode:
A diode is used for combining the signals, and isolating signals from a supply, they are the common use of diodes.
A diode is also used for converting AC from DC defined by the term rectifier.
A diode can be used as a snubber network and free-wheeling diode due to their high voltage and current characteristic.
The major use of the diode is to remove the negative signal from the AC current. This is called signal demodulation.