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

AZW file extension

Amazon Kindle eBook File

eBook Files

CSS file extension

Cascading Style Sheet

Web Files

DEM file extension

Video Game Demo File

Game Files

DWG file extension

AutoCAD Drawing Database File

CAD Files

INDD file extension

Adobe InDesign Document

Layout Files

M file extension

Objective-C Implementation File

Developer Files

M3U file extension

Media Playlist File

Audio Files

M4A file extension

MPEG-4 Audio File

Audio Files

MP4 file extension

MPEG-4 Video File

Video Files

MSI file extension

Windows Installer Package

Misc Files

PKG file extension

Mac OS X Installer Package

Compressed Files

SDF file extension

Standard Data File

Data Files

SITX file extension

StuffIt X Archive

Compressed Files

TOAST file extension

Toast Disc Image

Disk Image Files

WAV file extension

WAVE Audio File

Audio Files