What is Coefficient Of Performance?

Legal Definition
The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work required. Higher COPs equate to lower operating costs. The COP usually exceeds 1, especially in heat pumps, because, instead of just converting work to heat (which, if 100% efficient, would be a COP_hp of 1), it pumps additional heat from a heat source to where the heat is required. For complete systems, COP calculations should include energy consumption of all power consuming auxiliaries. COP is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.
-- Wikipedia
Legal Definition
Ratio of realized work or useful output per the amount of supplied effort or energy input. It is used typically as a measure of the energy efficiency. It is the basis for air conditioners, space heaters and other cooling and heating devices. COP equals heat delivered as output, shown in British thermal units (BTUs), per hour divided by the heat equivalent of the electric energy input. The latter is calculated to be one watt = 3.413 Btu/hour, or, alternatively, energy efficiency ratio divided by 3.413. The higher the COP, the higher the efficiency of the equipment.