The word grain has a great many meanings, most being descriptive of a small piece or particle. For examples:

• In geology, a grain is a single particle of rock or other material, such as sand or salt; see grain size.
• In agriculture, a grain is a type of simple dry fruit technically called a caryopsis. Such crops are often called cereals (grain can also refer to other types of seeds, though this is technically less correct).
• In materials science (especially metallurgy), a grain is a single crystal inside solid-state matter, also referred to as crystallite — related to the obsolete term "corn" as in corned beef.
• In photography, the fineness of image resolution for photographic film (i.e., graininess of a picture), originally related to the (crystallographic) grain size of silver iodide.
• In units of measurement, the grain is a unit of mass, which is used commonly for older drugs such as aspirin, for bullets, and for precious metals. One gram of metric weight equals 15.4323584 grains.
• In the context of wood or lumber, grain describes many varied aspects from personality or style to woodworking techniques (e.g. going against the grain).
• In golf, the direction in which individual blades of grass lie, usually in reference to a putting green.
• In rocket science, grain refers to the solid propellant of a rocket (either solid fuelled or hybrid), more or less a hollow cylinder, sometimes textured inside, and possibly very large.
• Grain may refer to the place Isle of Grain in Kent, England, on which lies the village of Grain, Kent.
• Grain is one of the stocks in the game Stock Ticker.
• In music, see granular synthesis.