A diode is an electronic component with two electrodes (connectors) that allows electricity to go through it in one direction and not the other direction.
Diodes can be used to turn alternating current into direct current (Diode bridge). They are used in power supplies and sometimes to decode amplitude modulation radio signals (like in a crystal radio). Light-emitting diodes (LEDs) are a type of diode that produce light.
Today, the most common diodes are made from semiconductor materials such as silicon or sometimes germanium.