Definition of field-effect transistor (FET)

a transistor in which the flow of current from source to drain is controlled by a charge applied to the gate. This charge attracts electrons into the area between source and drain or repels them away from it, thus changing its semiconductor properties. No current actually flows into the gate (in practice, there is a tiny current, on the order of 10^-12 ampere). Thus, field-effect transistors consume little power and can be packed very densely on integrated circuit chips.

MOSFETs (metal-oxide-semiconductor FETs) have an insulating layer of metal oxide between the gate and the rest of the transistor. They consume the least power of all kinds of transistors.