SEER is an acronym that stands for Seasonal Energy Efficiency Ratio. The SEER rating is a measurement of how much cooling capacity an AC has compared to its usage of energy. The cooling capacity is measured in Btu (British thermal units) per hour. It is compared to the rate of energy input, measured in watts. In other words, the SEER rating lets you know how much output (cooling capacity) the AC will have compared to its input (energy use). This lets you know how energy efficient the AC unit is. It can guide you in making a smart purchasing decision.