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

ASF file extension

Advanced Systems Format File

Video Files

BAK file extension

Backup File

Backup Files

CPP file extension

C++ Source Code File

Developer Files

DLL file extension

Dynamic Link Library

System Files

DTD file extension

Document Type Definition File

Developer Files

DWG file extension

AutoCAD Drawing Database File

CAD Files

INDD file extension

Adobe InDesign Document

Layout Files

JSP file extension

Java Server Page

Web Files

KML file extension

Keyhole Markup Language File

GIS Files

MDF file extension

Media Disc Image File

Disk Image Files

MP4 file extension

MPEG-4 Video File

Video Files

PNG file extension

Portable Network Graphic

Raster Image Files

SAV file extension

Saved Game

Game Files

TIF file extension

Tagged Image File

Raster Image Files

3DS file extension

3D Studio Scene

3D Image Files