Triode

In general an electronic component that has three electrodes, though the term triode is almost always used in reference to a particular configuration of vacuum tube possessing three electrodes: cathode, grid, and anode (usually referred to as the plate). The triode is the simplest tube design that can be easily used as in an amplifier circuit. Many tubes have other elements in them (control grid, screen grid, etc.) to more finely tune and control their operation.