Dictionary.net

Substances which are of little or no nutritive value, but are used in the processing or storage of foods or animal feed, especially in the developed countries; includes ANTIOXIDANTS; FOOD PRESERVATIVES; FOOD COLORING AGENTS; FLAVORING AGENTS; ANTI-INFECTIVE AGENTS (both plain and LOCAL); VEHICLES; EXCIPIENTS and other similarly used substances. Many of the same substances are PHARMACEUTIC AIDS when added to pharmaceuticals rather than to foods.

It can be dyes for color, scents, and prolonged shelf life of elements. Anything not nutritionally needed to make a product last longer or taste better. It is added on purpose but is not nutritionally necessary.