It means that an appliance is energy efficient and uses lower amounts of energy then normal. The lower the number the more cost efficient it is to run.
On things like windows, it means they better insulate your house.
Energy Star ratings are on just about every type of product you can think of if it has anything to do with energy usage. Whether directly or indirectly. Depending on who you are, like a homeowner for example, and where you live, you can get government rebates for buying products with energy star ratings on them.
I see, thanks for the answer. I would like to know more about it. Is it difficult to get an energy star rating? What are the standards that have to be met to be considered to be energy star?
Each product has a different set of standards they must meet. It is not really difficult to get the rating. Problem with that is that some people have created fake products to use to get the rebate.
What is an Energy Star Rating? 
Linear Mode
