The coefficient of performance is a ratio of the actual energy used for heating or cooling to the energy supplied for the process. For A/C units, coefficient of performance is given as an energy efficiency ratio and is defined as the cooling power divided by the electrical energy used.
In heating, the useful quantity is the heat supplied by the heat pump, while in cooling the useful quantity is the heat extracted by the refrigerator. The energy efficiency ratio that is used by manufactures compares performance of A/C units. It is simply the coefficient of performance but with the heat extracted given in terms of BTU/hour instead of watts.