Tests need to be carried out to determine the energy rating of appliances and products. These tests will rate their energy efficiency on a scale of A to G. If a product has an 'A' energy rating, that means that they are deemed to be the most energy efficient product of its class - while G is the least efficient.
You may also encounter A+ energy ratings. What this means is that the product is 10% more energy efficient than the average efficiency range of A.