Legally, food labeled "natural" does not contain any artificial ingredients, coloring ingredients, or chemical preservatives, and, in the case of meat and poultry, is "minimally processed." Sounds good. But what does all that really mean?
Meat from animals treated with artificial hormones can (and is) labeled "natural," as is meat injected with saline solution (claimed to add flavor, which it does, but it also adds considerable weight to a product sold by the pound). For more about meat labeling, see What Do Meat Labels Mean? for complete explanations.
Similarly, foods containing "natural flavors," such as processed proteins that you may or may not consider desirable, can legally sport the label "natural."
In short, the "natural" label on food means something and there are guidelines about which foods can be labelled "natural," but they aren't very stringent. For people interested in pure foods and minimally processed or unprocessed foods, the "natural" label probably won't tell you what you want to know. Be sure to read the label for more information.