Some people can't digest the ingredient found in most breads which is called gluten. It makes they're stomachs puff out or constipated and sometimes people get sick from not being able to digest it properly. So they make things like breads and crackers that do not have the ingredient gluten for the people who can't digest gluten. That's why you see some things that say gluten free.
My dad is Gluten intolerant and some things that are gluten free are suprisingly tastier than the gluten version. Like gluten free blueberry muffins are so much better tasting in my opinion than its gluten sister or other relative.
gluten is a "glue" found in many grains, but when a product is "gluten" free, it has no gluten of the kind found in WHEAT, BARLEY or RYE. (Corn gluten, for example, is OK).
Persons who must have gluten free food may have an allergy. Worse, they may have an autoimmune response caused when the eat even a tiny bit of gluten. The autoimmune response will last 5 to 6 weeks and make them more susceptible to cancer, diabetes, thyroid disease and more..
Gluten-free is what you HAVE TO be if you have Celiac disease. It's what is in wheat, barley, and rye that some people can't tolerate. It's not a choice for people who have Celiac disease, but lots of other people who don't think it's COOL to go gluten-free. But, if you have the disease, eating or drinking ANYTHING with gluten in it can kill you over time because it damages your small intestine.