What makes an appliance an energy star appliance?

What is the difference between an appliance classified as energy star and one that is not? What about it exactly makes it energy star?|||appliances have engery star ratings * or "C" worst energy appliance ***** or "AAA" the best energy appliance, meaning the energy efficency of the particular machine at what it's doing.|||If you Google Energy Star you will find the DOE website that defines the performance standards for each kind of appliance but generally, and energy star wastes less energy.