Biff,
As far as I know, three categories exist:
synthetic flavoring---created in a chemist's lab
natural flavoring---no synthetic ingredients
organic flavoring---all ingredients certified organic by the USDA standards
Those categories do not apply to PG, VG, PGA, or nicotine liquid, I believe. If a juice is advertised as "Organic," that designation refers to the flavorings only, not the bases. Vendors who sell Natural and/or Organic juices tend to be much pickier about the "purity" of their bases and nicotine, however.