Gluten (from Latin '' "glue") is a composite of the proteins gliadin and glutenin''. These exist, conjoined with starch, in the endosperms of some grass-related grains, notably wheat, rye, and barley.

A gluten-free diet is a diet completely free of ingredients derived from gluten-containing cereals: wheat (including kamut and spelt), barley, rye, and triticale, as well as the use of gluten as a food additive in the form of a flavoring, stabilizing or thickening agent.