Gluten is a mixture of vegetable proteins and proteins of prolamins and glutelins. In wheat the prolamins part of the proteins is gliadin and the gluten part is glutelin. In other cereals you may find other kinds of prolamins and lutelins i.e. different combinations of gluten and its components. In a laic interpretation, the term gluten is considered the protein from wheat, spelled, rye and barley.