What is meant by dietary supplement?

In addition to diet. It means adding vitamins and minerals to your daily food intake that you may not be getting in your regular diet. I prefer getting my vitamins and minerals through whole foods like raw fruits and veggies rather than taking man made synthetic vitamins that come in a jar. We need 7-13 servings of raw fruits and veggies daily.
2 meanings. First as colleagues say--vits & mins (and a few others, like omega 3 fatty acids) which should be added to one's diet in pill form--if diet is poor. Second a very long list of chemicals, natural, extracted or synthesized that are supposed to improve health and slow aging. The evidence for the value of these imo run the gamut from absent (many) through sparse (most) to convincing (a few).