SEER stands for Seasonal Energy Efficiency Ratio. It is used to indicate the efficiency of air conditioning systems. The higher the SEER number, the more cooling you get per unit of energy. As of January 2006, only units with a SEER of 13 or higher will be allowed to be sold in the United States. Today’s cooling units are up to 40% more efficient than those made as recently as 10 years ago. SEER is only one way to judge efficiency. Some better factors to look at are EER.