Seasonal Energy Efficiency Ratio (SEER) determines how energy efficient an air conditioner is per season/region. While EER is a better rating for smaller units, SEER rates larger appliances such as central air conditioning units. The more cool (or hot) air the system puts out for each unit of energy consumed, the higher the rating means higher energy efficiency.
According to the government, the lowest SEER score a unit may have is 13, but this number is increasing as we move towards more energy efficient appliances. In order for a unit to receive an ENERGY STAR rating, the unit must be ranked at a minimum of 14.
It is more logical for someone in a warmer climate, such as Florida, to invest in a high SEER air conditioner as opposed to someone who lives in the North East where there are only a few months of warm temperatures per year. Since the A/C unit tends to run longer in warmer climates, energy efficiency will be critical to keeping your energy bills lower and decreasing the impact on the Earth.