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

PKG file extension

Mac OS X Installer Package

Compressed Files

CFG file extension

Configuration File

Settings Files

SYS file extension

Windows System File

System Files

M4A file extension

MPEG-4 Audio File

Audio Files

TMP file extension

Temporary File

Backup Files

ISO file extension

Disc Image File

Disk Image Files

CLASS file extension

Java Class File

Developer Files

AVI file extension

Audio Video Interleave File

Video Files

DLL file extension

Dynamic Link Library

System Files

PL file extension

Perl Script

Developer Files

GPX file extension

GPS Exchange File

GIS Files

DRV file extension

Device Driver

System Files

CPL file extension

Windows Control Panel Item

System Files

ASX file extension

Microsoft ASF Redirector File

Video Files

7Z file extension

7-Zip Compressed File

Compressed Files