Barley is a grain used as a staple food, as well as animal feed. It is often used in soups and stews as a whole grain (actually, with the hull removed but the bran remaining) or as pearl barley (with the bran removed also). It is malted and crushed for making beer and other malt products. It is ground to flour for making bread, both raw and malted.
Barley is not gluten free. Whilst it does not have the same form of gluten much loved by bread bakers, it has a protein called hordein which is equally harmful to people sensitive to gluten, including those with coeliac disease.