filename extension

Also found in: Dictionary, Thesaurus, Medical, Legal, Financial, Acronyms, Wikipedia.

filename extension

(filename extension)
The portion of a filename, following the final point, which indicates the kind of data stored in the file.

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. Graphics formats.
References in periodicals archive ?
It replicates under Windows 95, Windows 98, and Windows NT systems and infects Windows programs with EXE (executable) and SCR (screen savers) filename extensions, as well as Windows KERNEL32.
1 compliance -- MIME-typing supported through filename extensions -- Imagemap support -- Event logging with common log format -- Directory indexing -- Virtual hosting.