SEER (Seasonal Energy Efficiency Rating)
SEER is an abbreviation for Seasonal Energy Efficiency Rating. It is the most commonly used measure of the efficiency of consumer central air conditioning systems. (EER, or Energy Efficiency Rating is the most commonly used measure of efficiency for commericial air conditioning systems.)
As of January, 2006, an air conditioner must have a SEER of at least 13 to be sold in the United States. Higher efficiency models have a SEER of up to 21.