A (typically) three-character addition to a computer file name. With some computer platforms (in particular, DOS), the name of a file is limited to eight characters, followed by a period and a three-character extension (such as "FILENAME.EXT"). The extension is often used to indicate the file format in which the file was saved. Some common extensions used for graphics files include ".eps" (encapsulated PostScript), ".pct" (PICT), ".tif" (TIFF), etc. File extensions are useful means of indicating and determining file type. Also known as a file-name extension.
Many common file extensions used in DOS, Windows, and OS/2 include:
AIAdobe Illustrator
AIFAudio Interchange File Format
BAKBackup copy of an edited file
BMPBitmap graphic
CDRCorel Draw vector graphics
CMDOS/2 command file
COMDOS command file
DOCASCII text document
DLLDynamic link library
EPSEncapsulated PostScript file
EXEExecutable file, or machine language file
GIFGraphics Interchange Format file
HLPHelp file
ICOIcon
INIInitialization file
JPGJPEG file
MIDMIDI file
PCTPICT file
PCXZsoft bitmap file
PDFPortable Document Format file
PIFProgram Information File
PSPostScript file
SEAStuffIt self-expanding archive
SITStuffIt (compressed) archive)
SYSOperating system component
TEXTEX or LATEX document
TGATARGA graphics file
TIFTIFF graphics file
TMPTemporary file
TXTASCII text file
WAVSound wave file
WKQQuattro spreadsheet file
WMFWindows MetaFile
WKSLotus 1-2-3 worksheet file
XLSMicrosoft Excel worksheet file
ZIPPKZIP-compressed file