The Coefficient of Performance (COP) of a heat pump is essentially the same concept as the thermal efficiency of a boiler (e.g., the desirable output divided by the necessary input). For a heat pump, this would be the rate of heat output from the heat pump divided by the rate of energy input (as electricity) to operate the heat pump.
Consider, for example, a heat pump that releases 48,000 Btu/h to the load, while drawing 4,500 watts of electrical power. Its COP could be calculated as shown in Formula 1.