Oat flour is a flour which is made from ground oats. This flour can be used in a wide variety of recipes, although it does carry a caution, as it does not behave like wheat flour, since it contains no gluten. As a result, if oat flour is used alone, baked goods will not rise or hold together; oat flour must be mixed with other flours in baking.
Many people use oat flour in gluten-free baking. It is important to remember that oat flour is often processed in facilities which handle gluten-containing grains, like wheat. As a result, it can be contaminated with gluten, and people who are extremely sensitive to gluten may experience discomfort if they consume products made with the contaminated oat flour. It is a good idea to purchase oat flour which is labeled as gluten free if this is a concern.
Oats can go rancid, and as a result they are usually cooked before processing to make them more shelf stable. In the case of oat flour, it is a good idea to use flour which is as fresh as possible. You can store it in an airtight container in a cool, dry place, or you can freeze it to extend the shelf life; frozen oat flour is very easy to use, and it will be less likely to go bad if you only use a small amount of oat flour at a time.