Why A field-effect transistor (FET) has three terminals named gate, source, and drain. The voltage on the gate creates an electric field that widens or narrows the conducting channel between source and drain, controlling current with essentially no gate current. That is different from a bipolar transistor, which is controlled by base current.
Watch out The bipolar junction transistor is the tempting choice, but its three terminals are the base, emitter, and collector. A varistor is a voltage-dependent resistor, not a transistor, and a Hall-effect device is a magnetic field sensor.
FET = Gate, Drain, Source. BJT = Base, Emitter, Collector. Gate means field-effect.