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

CSR file extension

Certificate Signing Request File

Web Files

DLL file extension

Dynamic Link Library

System Files

MP4 file extension

MPEG-4 Video File

Video Files

ASP file extension

Active Server Page

Web Files

MSI file extension

Windows Installer Package

Misc Files

GIF file extension

Graphical Interchange Format File

Raster Image Files

7Z file extension

7-Zip Compressed File

Compressed Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

BAK file extension

Backup File

Backup Files

FNT file extension

Windows Font File

Font Files

XCODEPROJ file extension

Xcode Project

Developer Files

VOB file extension

DVD Video Object File

Video Files

RA file extension

Real Audio File

Audio Files

DEM file extension

Video Game Demo File

Game Files