Questions about ways to measure and improve the ability to get useful work out of devices that consume energy. This includes coal, oil and gas as well as electricity.
Devices that consume energy, or energy dense materials (fuel) will always "lose" some of the energy. This means that - for example - a furnace burns fuel to heat air. Not all of the heat the fuel generates by burning will make it into the air, some is wasted because of inefficient design.
It is a constant effort on the part of manufacturers, designers and researchers to come up with more efficient devices.