An acronym for Field Effect Transistor. It is a bipolar transistor is a current amplifying device. An input current results in an amplified output current Hfe=Ic/Ib, where Ic is the output or collector current and Ib is the input or base current. The FET on the other hand is a transconductance device, that is an input voltage results in an output current G=Id/Vg, where Id is the output or drain current and Vg is the input or gate voltage. This assumes a common emitter connection for the bipolar transistor and a common source connection for the FET.