Gluten flour is refined gluten protein, used to strengthen flour as needed. To make wheat gluten requires separating wheat flour into starch and protein by rinsing the starch away, leaving raw gluten which can be used in recipes. It can also be dried, as is the case for vital wheat gluten.
It can be used to make a vegetarian meat substitute known as seitan. Adding ~1 tsp of gluten flour per cup of All purpose flour gives the resulting mix the protein content of bread flour. Adding it to wholegrain bread recipes improves the texture and elasticity of the dough, helps retain the gas and steam from baking, and gives more volume to the baked bread.
Flour is a powder made by grinding raw grains, roots, beans, nuts, or seeds. It is used to make many different foods. Cereal flour is the main ingredient of bread, which is a staple food for most cultures. Wheat is the most common base for flour, as is corn flour and rye flour. Cereal flour consists either of the endosperm, germ, and bran together (wholegrain wheat flour) or of the endosperm alone (all purpose flour).