A Field Effect Transistor (FET) is a type of transistor that controls the flow of electrical current using an electric field. It has three main terminals: the source, the drain, and the gate. The voltage applied to the gate terminal influences the conductivity of a channel between the source and drain, allowing the FET to act as a switch or amplifier. FETs are widely used in electronic devices due to their high input impedance and low power consumption. They come in various types, including MOSFETs (Metal-Oxide-Semiconductor FETs) and JFETs (Junction FETs), each with specific applications in circuits and systems.