Vital wheat gluten is made from wheat flour which  is hydrated to activate the gluten, the main protein in wheat. Then everything but the gluten is removed. The gluten is then dried and ground back into a powder. It's the main ingredient in seitan recipes like this one, but is also great when used as a binder in vegan meatloaf and burgers. I use it in the "meatball" recipe in my cookbook Vegan Comfort Cooking. It's also a useful ingredient in bread recipes. Just a tablespoon or two in a loaf can improve the texture and elasticity of dough, which in turn helps improve the rise, crumb and the crust. It's especially useful when making bread with lower protein flours such as wholewheat and rye. Vital wheat gluten pretty cheap to buy although not all grocery stores carry it. I buy mine from Amazon. This is the one I used to make my seitan. It's incredibly good value for a great big bag and it's non GMO. Pour it into an airtight container and leftovers will keep for ages and ages.