Diodes are semiconductor devices that allow current to flow in one direction while blocking it in the opposite direction. They are made from materials such as silicon or germanium and consist of a p-n junction, where p-type and n-type semiconductors meet. When a diode is forward biased (positive voltage applied to the p-side), it allows current to flow easily. In contrast, when reverse biased (positive voltage applied to the n-side), it blocks current flow, except for a small leakage current. Diodes have various applications, including rectification in power supplies, signal demodulation, and voltage regulation using Zener diodes. Understanding the characteristics and functions of diodes is essential for designing and analyzing electronic circuits.