The FDA finally approved an official Gluten Free label to begin appearing on products beginning next year. In order to be able to use it:

…gluten free foods can’t contain more than 20 parts per million of gluten. Below that level gluten can’t be detected reliably….According to the FDA, most gluten-free food on the market already meets this standard. It goes into effect one year from now.

Some 3 million people have celiac disease in the U.S, in addition there are an estimated 18 million who have gluten sensitivity. Source: NPR.

Here is a link to the official press release from the FDA.