A Gas Discharge Tube (GDT) is an electrical component used to protect circuits from voltage surges. It consists of a sealed glass or ceramic tube filled with a low-pressure gas. When the voltage exceeds a certain threshold, the gas ionizes, allowing current to flow and diverting excess energy away from sensitive components. GDTs are commonly used in surge protection devices, such as those found in telecommunications and power systems. They are effective at clamping high-voltage spikes, making them essential for safeguarding equipment from lightning strikes and other transient voltage events.