Bran, also known as miller's bran, is the component of a cereal grain consisting of the hard layers - the combined aleurone and pericarp - surrounding the endosperm. Corn (maize) bran also includes the pedicel (tip cap). Along with the germ, it is an integral part of whole grains, and is often produced as a byproduct of milling in the production of refined grains. Bran is highly nutritious, but is difficult to digest due to its high fiber content; its high fat content also reduces its shelf life as the oils/fats are prone to becoming rancid.
https://en.wikipedia.org/wiki/Bran