Energy Star is an international standard for the energy efficiency of consumer electronics products. It was originally a US Government program in the 1990s, but other countries in Asia and Europe have also adopted the program.
Energy Star-rated products include computers, appliances, HVAC, lighting, and home electronics. TV's that are Energy Star-compliant are often 20-30% more efficient (as in they use that much less electricity) than non-compliant products.
Certain states, like California, use the Energy Star specifications to limit the power consumption of TVs sold in the state. The most noticeable aspect to the end user with Energy Star-rated televisions (other than the reduced power consumption) is the initial setup menu for the TV includes "Store" and "Home" options. Selecting "Home" puts the TV in a lower power mode that is always better looking in a home setting than the "Store" mode.