(n) a string of characters beginning with a period and followed by one or more letters; the optional second part of a PC computer filename, Syn. filename extension, file name extension, Example:most applications provide extensions for the files they create; most BASIC files use the filename extension .BAS
(n) (computer science) the name given to a computer file in order to distinguish it from other files; may contain an extension that indicates the type of file, Syn. computer file name, computer filename, file name