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

AVI file extension

Audio Video Interleave File

Video Files

CFM file extension

ColdFusion Markup File

Web Files

CS file extension

Visual C# Source Code File

Developer Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

EPS file extension

Encapsulated PostScript File

Vector Image Files

GBR file extension

Gerber File

Data Files

INDD file extension

Adobe InDesign Document

Layout Files

MDB file extension

Microsoft Access Database

Database Files

MOV file extension

Apple QuickTime Movie

Video Files

MP4 file extension

MPEG-4 Video File

Video Files

PSD file extension

Adobe Photoshop Document

Raster Image Files

PSPIMAGE file extension

PaintShop Pro Image

Raster Image Files

RSS file extension

Rich Site Summary

Web Files

SAV file extension

Saved Game

Game Files

THM file extension

Thumbnail Image File

Raster Image Files