Grains are seeds of grasses. More particularly, the term "grains" usually refers to the cereal grains, those that are used as food or fodder by humans. Three grains—rice, wheat, and corn—are the major source of calories in the human diet throughout the world, both through direct consumption or by providing animal feed. In addition, corn is a significant source of raw materials for some segments of the chemical industry.
Like other seeds of flowering plants, grain contains both the embryo and endosperm . The diploid embryo, often called the germ, contains the tissues that develop into the new individual after germination. The triploid endosperm is a rich nutritive tissue formed by the fusion of a second sperm and the two nuclei of the central cell in the embryo sac. Surrounding both endosperm and embryo is the protein - and oil-rich aleuronic layer. This layer plus several thin outer coverings and the remains of the seed coat make up the bran.
Grains are grown in greater quantities worldwide than any other type of crop and provide more food energy to the human race than any other crop. In some developing nations, cereal grains constitute practically the entire diet of common folk. In developed nations, cereal consumption is more moderate but still substantial. The word cereal derives from Ceres, the name of the Roman goddess of harvest and agriculture. Grains are traditionally called corn in the United Kingdom, though that word became specified for maize in the United States, Canada, New Zealand, and Australia.