Grain refers to the small, hard seeds harvested from cereal crops, such as wheat, corn, rice, and barley. These seeds are a primary source of food for humans and animals, providing essential nutrients like carbohydrates, proteins, and vitamins. Grains can be processed into various products, including flour, bread, and cereals. Grains are typically classified into two categories: whole grains and refined grains. Whole grains contain all parts of the seed, offering more fiber and nutrients, while refined grains have been processed to remove the bran and germ, resulting in a finer texture but fewer health benefits.