Gluten is the name given to a group of proteins (also known as prolamins). Reactions to this group of proteins are not considered to be a true IgE allergic reaction.
Coeliac disease (European spelling, known as Celiac in North America) is an autoimmune disorder where the body reacts to gluten in foods consumed and damages the gut, causing poor absorption of foods.
Despite not being an allergy gluten is usually included in food allergy lists as it needs to be labelled on food in Europe as there are large number of sufferers worldwide.
Coeliac disease is not an allergic condition, but is triggered by gluten found in cereals and grains.