Diodes are semiconductor devices that allow the flow of electrical current in one direction while blocking it in the opposite direction. They have a p-n junction, which is the boundary between a p-type semiconductor (with an excess of positively charged holes) and an n-type semiconductor (with an excess of negatively charged electrons).
When a diode is forward-biased (connected to a voltage source in the direction of its forward current), it conducts electricity easily, allowing the current to flow through. When a diode is reverse-biased (connected to a voltage source in the direction of its reverse current), it blocks the current flow, acting like an insulator. Diodes are used in a variety of applications, such as rectification, voltage regulation, signal detection, and protection from voltage spikes.