A diode is an electrical component made to only allow one way of electric current to flow. Each of its two extremities (or terminals) has an anode with a distinct charge. In contrast to the negatively charged "cathode," the "anode" end has a positive charge. Natural current always moves from the electrode to the cathode.

Commonly used as switches, diodes enable or block the passage of electricity. For instance, in an electrical circuit, electricity can be halted by merely flipping an active diode. The diode can be flipped back to its initial orientation to resume conducting electricity through the circuit. A circuit can employ multiple diodes as logic switches to carry out AND and OR operations.

Although a diode's current typically travels in one way, this can occasionally happen. Negative voltage applied to a diode must be greater than the "breakdown voltage" for the current to start moving the other way. A normal diode's breakdown voltage is between -50 and -100 volts, though it can be considerably less or more depending on the diode's construction and components. While some diodes are made to enable current to travel in both ways, others can be harmed by the backward passage of current. For instance, zener diodes are made with particular failure voltages for various uses.

The light-emitting diode, or LED, is another popular form of diode. Visible light is produced by light-emitting diodes when current flows between the anode and cathode through a region known as the p-n junction. Depending on the electrical charge and the materials used in the diode, the light produced by the electrical charge in this area has a variety of hues.