a device which does something. It is nearly always a source of emf, but its important property could be that it is sending a signal of some kind. (See also passive device.)

Devices such as transistors, integrated circuits and vacuum tubes that require an external power source in order to perform an intended purpose, such as amplification.

A component that has gain or operates in a non-linear fashion to change the basic character of an electric signal by, for example, amplification or rectification, or a device comprised of such component, for example a transistor switch. A device whose output is dependent upon an external source of power other than the input signal.

A device capable of producing gain; for example, transistors, and ICs.

A device or circuit capable of some dynamic function, such as amplification, oscillation, or signal control, and which usually requires a power supply for its operation. An amplifier is an example of an active device.

A device that requires a source of energy for its operation and has an output that is a function of present and past input signals. Examples include power supplies, transistors, LEDs, Lasers, Detectors, amplifiers, and transmitters.

A device that has an input(s) which controls a power supply to the device.

A device that is not in the suspend state and is powered on.

Active devices are energy controllers, sometimes converting one form of energy to another: chemical, hydraulic, thermal energy, mechanical , nuclear, solar, etc, into electrical energy, driving electrical current around the circuit and hence delivering continuous energy to it.