Gluten is a natural protein that occurs in wheat/barley/rye flour, and can also be found in some cosmetic products. It gives elasticity to dough and creates a chewy texture for bread. Some people have an intolerance to gluten, particularly those with a what allergy or those suffering from coeliac disease because the immune system has an adverse reaction to it. A gluten intolerance can cause bloating, constipation, diarrhea, and joint pain.
Although gluten is found in many processed foods made from wheat flour (such as most breads, biscuits and pastas) fortunately these days there are many gluten-free products available in health food shops, and even in many supermarkets. Therefore, even if you do discover that you're gluten intolerant you'll still be able to enjoy many of your favourite foods. If you're planning to eat out, some restaurants also offer gluten-free options. ,
From what I understand, Gluten is a protein found in flour. I have heard that this protein has been added in recent years because of mass production of bread. I have no idea how true this is, but it would be one of the reasons why there are more people suffering from consuming Gluten. I personally found that eating bread gives me stomach cramps. That also goes for many other flour base products. Of course, it is not fatal, however I try to avoid bread as much as possible.