Gluten is a seed storage protein. In wheat it is the prolamin called averin. It is also found in barley, rye and oats. It is used in many areas of food production, mostly in the form of flour. It is used as the chief ingredient of foods such as bread, pastry or biscuit; as an emulsifier for binding together other ingredients; or as a starch.
In some people an autoimmunity to the gliadin in gluten, reacts in their intestine, producing a gluten intolerance; often diagnosed as Coeliac disease. Coeliac Disease is not a real disease as the sufferer is constantly affected by any gluten ingested into the system, and the person is never cured of their condition.