The term "natural" has not been defined in FDA's law (the Federal Food, Drug, and Cosmetic Act) or in FDA's regulations.
However, USDA's Agricultural Marketing Service, who oversees the National Organic Program, published the final rule on national organic standards on December 27, 2000. Implementation of the program began in April 2001. A press release on these standards can be found at: http://www.usda.gov/news/releases/2000/12/0425.htm
Answers to Frequently Asked Questions (FAQ's) about the National Organic Program (NOP) can be found at: http://www.ams.usda.gov/nop/Q&A.html
Source: USDA Agricultural Marketing Service, August 2001