Gluten is the protein found in wheat, and many other grains such as rye and barley.
Wheat is a grain that contains gluten. All wheat has gluten in it.
It is recommended for people diagnosed with coeliac disease to follow a strict gluten free diet.
However, those with IBS, gluten intolerance and other stomach issues, diets can vary depending on the person. I am gluten intolerant, but not off the charts like I am with dairy. Therefore, I usually follow an 80/20 diet. This means that 80% of the time I am gluten free, but allow myself small cheats such as a small piece of bread or a wholewheat wrap. Spelt flour has a small amount of gluten and is easier to digest, that is why I use spelt flour in recipes.
Beer contains gluten and barley. There is now Gluten Free beer popping up, brewed from other grains such as millet and buckwheat. Low gluten beers would be made from barley and rye rather than wheat.