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

GADGET file extension

Windows Gadget

Executable Files

CUE file extension

Cue Sheet File

Disk Image Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

7Z file extension

7-Zip Compressed File

Compressed Files

COM file extension

DOS Command File

Executable Files

M3U file extension

Media Playlist File

Audio Files

MPG file extension

MPEG Video File

Video Files

CPL file extension

Windows Control Panel Item

System Files

ASF file extension

Advanced Systems Format File

Video Files

DLL file extension

Dynamic Link Library

System Files

MOV file extension

Apple QuickTime Movie

Video Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

CLASS file extension

Java Class File

Developer Files

TTF file extension

TrueType Font

Font Files