File extensions – definition and basic information


File extensions are the integral parts of the files that are on each computer. Often, when working on a computer, we encounter a wide range of files, such as docx, ppt, part, mp3 or rmvb. We realize that they are there – but we often do not know what they are for on our computer.

File extension, also known as the filename extension is a suffix added to the name of a computer file, usually consisting of a number of characters placed after the last dot in the filename, which gives us information about its coding. In other words a file extension is a file format. It allows the operating system (e.g. Windows) to recognize what program it should try to open the file.

In the table below you will find a random selection of popular file extensions.


File extension The full name of the file Category

ASX file extension

Microsoft ASF Redirector File

Video Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

H file extension

C/C++/Objective-C Header File

Developer Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

INDD file extension

Adobe InDesign Document

Layout Files

INI file extension

Windows Initialization File

Settings Files

KML file extension

Keyhole Markup Language File

GIS Files

M4A file extension

MPEG-4 Audio File

Audio Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

PIF file extension

Program Information File

Executable Files

RTF file extension

Rich Text Format File

Text Files

TAR file extension

Consolidated Unix File Archive

Data Files

TMP file extension

Temporary File

Backup Files

XLR file extension

Works Spreadsheet

Spreadsheet Files

3G2 file extension

3GPP2 Multimedia File

Video Files