расширение имени файла необязательная часть имени файла, следующая за точкой. Обычно содержит от одного до трёх символов, дополняющих само имя (например, read.me), либо указывающих на тип файла, т. е. на тип хранящихся в нём данных Смотри также: 8.3, associate, default extension, double extension, filename, filespec, LFN
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.