米糠是稻米加工中碾米工序得到的一种黄色的皮层，它是稻米果实的皮层。也被称为“米皮”、“清糠”。入药用的谷糠，多指米皮糠而言。一般中药选用的是米皮糠的内衣，中医称为「杵头糠」，又称「谷白皮」。内服药用一般以杵头糠为主，谷糠外皮较少用。

稻谷在脱粒脱壳后得到糙米，糙米是完整的水稻果实。而我们通常所食用的稻米是指的是加工后的精米，它是水稻种子的胚乳部分。在从糙米到精米的过程中抛弃掉的部分就是米糠。

米糠包括稻米的外果皮、中果皮、交联层、种皮，有些地方还包括胚芽，而有些地方的称呼中包含颖壳（稻谷的壳）。

米糠的化学成分主要是糖类、脂肪和蛋白质，此外还含有维生素等成分。

Bran, also known as miller's bran, is the hard outer layers of cereal grain. It consists of the combined aleurone and pericarp.

Along with germ, it is an integral part of whole grains, and is often produced as a byproduct of milling in the production of refined grains. When bran is removed from grains, the grains lose a portion of their nutritional value. Bran is present in and may be milled from any cereal grain, including rice, corn (maize), wheat, oats, barley and millet. Bran should not be confused with chaff, which is coarser scaly material surrounding the grain, but not forming part of the grain itself.