A defined chemical compound, whether extracted from nature or synthesized, that is perceived by the nose as an odor and used to build flavors and fragrances. The flavor industry works with thousands of them: vanillin for vanilla, isoamyl acetate for banana, benzaldehyde for almond, each a single molecule carrying a recognizable scent. Natural and synthetic versions are chemically identical when the structure matches, differing only in origin, cost, and labeling implications. Flavorists blend aroma chemicals the way painters mix pigments, constructing the cherry of a soda or the butteriness of a pastry from dozens of components in precise ratios. Safety evaluation treats each as an individual substance with its own toxicological profile and permitted use levels, making this molecular approach to flavor both an art and a regulated science.