Power is the work input.
For a lighting system, the power is the wattage of the system. A 60 watt incandescent lamp uses 60 watts of power to operate. Since utilities measure usage for an entire building, they use kilowatts or thousands of watts. So a utility would measure the 60 watt lamp as .06 kW. Utilities refer to the monthly kW reading as demand . Utilities factor in the amount of time power is used, typically in hours.