What do EER and COP stand for?

An air conditioner's efficiency is measured using the Energy Efficiency Ratio (EER) for cooling and Coefficient of Performance (COP) for heating.

They indicate the ratio of cooling or heating provided by a unit relative to the amount of electrical input required to generate it. Air conditioners with a higher EER and COPS value are more efficient, so by comparing COP and EER ratios of products with the same capacity output you can determine which is more energy efficient.