Field Effect Transistor (FET) is a transistor in which the resistance of the source to drain current path is changed by applying a transverse electric field to the gate terminal. It uses an electric field to control the electrical behaviour of the device. FETs are also known as unipolar transistors since they involve single-carrier-type operation.
Field effect transistors generally display very high input impedance at low frequencies. The conductivity between the drain and source terminals is controlled by an electric field in the device, which is generated by the voltage difference between the body and the gate of the device.