Shell

Things commonly known as shell include:

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• An animal shell, the hard, rigid outer covering of an animal such as a mollusk or a turtle.
• The hard outer layer of some plant fruiting bodies such as nuts.
• A type of user interface in computer software, often an operating system shell, such as a Unix shell command line interpreter in the Unix operating system or the DOS Shell in MS-DOS. See shell (computer science).
• An electron shell (energy level), consisting of a number of electrons in an orbital around an atomic nucleus
• The short name (and Brand) of the Royal Dutch Shell Energy multinational.
• A projectile with explosive charge, shot from a gun; typically shells are larger than bullets and shot from larger guns. See shell (projectile).
• In physics, see On shell and off shell
• A structural form, usually made of concrete, that principally derives its strength by virtue of its shape. The term is derived from the primary usage in the context of nature. For example, the shell of an egg though very thin is difficult to break because of its shape.
• A long, narrow, rowed watercraft. See racing shell.
• A sorting algorithm invented by Donald L. Shell. See shell sort.