filename extension

Computing Dictionary

filename extension definition

filename extension
The portion of a filename, following the final point, which indicates the kind of data stored in the file - the file type.
Many operating systems use filename extensions, e.g. Unix, VMS, MS-DOS, Microsoft Windows. They are usually from one to three letters (some sad old OSes support no more than three). Examples include "c" for C source code, "ps" for PostScript, "txt" for arbitrary text.
NEXTSTEP and its descendants also use extensions on directories for a similar purpose.
Apart from informing the user what type of content the file holds, filename extensions are typically used to decide which program to launch when a file is "run", e.g. by double-clicking it in a GUI file browser. They are also used by Unix's make to determine how to build one kind of file from another.
Compare: MIME type.
Tony Warr's comprehensive list (http://camalott.com/~rebma/filex.html).
FAQS.org Graphics formats (http://faqs.org/faqs/graphics/fileformats-faq/).
(2002-04-19)
The Free On-line Dictionary of Computing, © Denis Howe 2010 http://foldoc.org
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WordNet
filename extension

noun
a string of characters beginning with a period and followed by one or more letters; the optional second part of a PC computer filename; "most applications provide extensions for the files they create"; "most BASIC files use the filename extension .BAS" [syn: extension
WordNet® 3.0, © 2006 by Princeton University.
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