Gluten,in terms of celiac and when referring to a “gluten-free”diet,is a protein found in the endosperm of wheat and its relatives such as barley,rye and spelt.
Gluten is what gives doughs made with these grains their stretch and flexibility and it’s added to foods that are not normally gluten containing in order to alter texture or even to prevent food from sticking to itself. It helps things to be “chewy”and soft.
By definition,anything made with wheat,barley,rye or spelt contains gluten. Though I have heard of some highly refined extracts claiming to be gluten-free,I don’t buy that enough to take the chance. If the ingredient label says the product contains any of these grains,I don’t eat it.
Gluten can also be introduced to a food due to cross-contamination. This occurs when a gluten-free food is exposed to gluten,often on shared machinery or storage during processing or even when it is grown in fields next to a gluten-containing grain. Oats,in particular,tend to be highly susceptible to cross-contamination with gluten. If you have to be on a gluten-free diet,look for any note that the product you are considering is manufactured or processed it a plant that also processes any of the four grains I’ve listed. I don’t typically buy those items either unless the manufacturer/processor has a very strict policy of cleaning and a great track record. Even then,it’s a toss of the dice.
So gluten is a natural part of wheat,barley,rye and spelt but it’s strictly off-limits to a celiac.