Nutritional Yeast?

While doing some research on vegetarianism, looking for recipes mainly, I ran across the term "Nutritional Yeast" or "nooch" which is weird but oh well. You ever hear of it? If so, what brand do you like the most? All of these recipes I'm running across are making me want to eat them and overeating, even if it's on veggies, isn't a good idea. :/