Field-Effect Transistors:MOSFETs are 3-terminal devices characterized by a conductive channel (either p-type or n-type semiconductor) between 2 of the terminals (called source & drain), through which the current flow is controlled by an electric field due to an voltage applied to the 3rd terminal (called gate). The gate is insulated from the conducting channel—in fact, MOSFETs are sometimes called "Insulated-Gate FETs" or IGFETs—this blocked gate terminal results in a very high input impedance which is one of the most advantageous features of these devices over BJTs.