Processed oats may contain oat bran, or the bran can be removed and prepared separately. The cereal grain known as oat is the source of edible oats and oat bran.
Oats are processed into food products by removing the hulls, leaving the oat groats. The bran is the layer directly below the hull. When the bran is removed, what is left is far less nutritious than if the bran were left on.
Steel-cut oats are oat groats with the bran intact and chopped with steel blades, while old-fashioned (rolled) oats also still have the bran and are chopped, steamed and rolled. Quick-cooking and instant oatmeals usually have the oat bran removed.