Flour is the finely milled meal of cereal grains. The term mostly used to refer to wheat flour. However, nuts such as chestnuts, root vegetables like potatoes, seeds such as buckwheat and mung bean can also be made into flour. Wheat flour is a staple of European, North American, Middle Eastern, African and South Asian cuisines. It's graded according to whether it is made from hard wheat, soft wheat, or a mixture of the two; and whether the grain's bran and germ are removed or left in. It is normally used in dishes where raising agents are not required.
Wheat flour, and flours made from other grains such as rye and barley, contain gluten (a protein). Gluten gives dough its elasticity, leavening qualities and chewiness. Coeliacs, and those intolerant to gluten, should look for rice flour or non-wheat, gluten-free flours.