http://dietary-supplements.info.nih.gov/factsheets/dietarysupplements.asp
Office of Dietary Supplements, National Institutes of Health
A dietary supplement is a product (other than tobacco) that is intended to supplement the diet; contains one or more dietary ingredients (including vitamins; minerals; herbs or other botanicals; amino acids; and other substances) or their constituents; is intended to be taken by mouth as a pill, capsule, tablet, or liquid; and is labeled on the front panel as being a dietary supplement.