Extension

extension

(1) See domain extension.

(2) A software add-on. For example, see Firefox extension.

(3) Prior to Mac OS X, an executable module that enhanced the Mac operating system. The Windows counterpart is a "dynamic link library" (see DLL).

(4) A file type that is appended to the end of a file name. All executable programs in the Windows and Mac worlds use extensions: .EXE in Windows; .APP in Mac (see APP file). In the Unix/Linux environment, executables do not use an extension.

No matter which environment, data files have extensions; for example, a file with a .DOC extension is a Microsoft Word document. A file with a .JPG extension is a JPEG image.

Prior to Windows 95, Windows extensions had no more than three letters or digits. Starting with Windows 95, extensions could be considerably longer, but in practice are generally limited to only a few characters.

Common Extensions and Exhaustive Lists
In this encyclopedia, more than 500 common file extensions are listed under the terms "extension," followed by their first letter such as extension a, extension b and extension c. However, there are Web sites that catalog many more, including the most obscure; for example, visit www.filext.com. See Win Show file extensions, dangerous extensions and graphics formats. See also domain extension.

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extension

1. Commerce a delay, esp one agreed by all parties, in the date originally set for payment of a debt or completion of a contract

2. the property of matter by which it occupies space; size

3. Med a steady pull applied to a fractured or dislocated arm or leg to restore it to its normal position

4. 

a. a service by which some of the facilities of an educational establishment, library, etc., are offered to outsiders

b. (as modifier): a university extension course

5. Logic

a. the class of entities to which a given word correctly applies: thus, the extension of satellite of Mars is the set containing only Deimos and Phobos

b. conservative extension a formal theory that includes among its theorems all the theorems of a given theory

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extension [ik′sten·chən]

(mathematics)

extension fields

(physiology)

A movement which has the effect of straightening a limb.

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extension

A wing or structure added to an existing building.

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1.	(filename extension)	extension - filename extension.
2.	(programming)	extension - A feature or piece of code which extends a program's functionality, e.g. a plug-in.

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Extension 

in metalworking. (1) Hot deformation, in which the length of a billet is increased by decreasing the area of its cross section. Extension is performed on hammers and presses by successive pressings of the billet, with a rotation of 90° after each pressing.

(2) Cold sheet pressing, in which hollow components are made from sheets. Cold extension is used to make bushings, casings for instruments and apparatus, and cans and saucepans. The billet is usually cut from a sheet, with an allowance for diameter, and is pressed into the peripheral area of the matrix. Upon the subsequent movement of the puncheon, the middle, unpressed part of the billet is pressed into the opening in the matrix.