Gluten is a protein found in grains such as wheat, barley, rye and triticale (a cross between wheat and rye).
A gluten-free diet is used to treat celiac disease. Gluten causes inflammation in the small intestines of people with celiac disease. Eating a gluten-free diet helps people with celiac disease control their signs and symptoms and prevent complications.
read more: http://www.mayoclinic.com/health/gluten-free-diet/my01140