A gluten-free product only contains naturally gluten-free cereals with a gluten content of less than 20mg/kg (EU regulation).
A gluten-free diet involves eliminating the gluten in foods that contain wheat, rye, or barley. Such grain products are replaced with gluten-free crops such as rice, corn, buckwheat, millet, quinoa, and gluten-free oats.
Coeliac disease is an autoimmune disorder caused by gluten found in wheat, barley and rye. It's relatively common and a gluten-free diet is the only treatment for coeliac disease, which is a lifelong condition.
For other diseases, a gluten-free diet can also help. People with irritable bowel syndrome or inflammatory bowel disease can also benefit from a gluten-free diet.