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

VOB file extension

DVD Video Object File

Video Files

ZIP file extension

Zipped File

Compressed Files

WMV file extension

Windows Media Video File

Video Files

BAK file extension

Backup File

Backup Files

7Z file extension

7-Zip Compressed File

Compressed Files

CPL file extension

Windows Control Panel Item

System Files

CER file extension

Internet Security Certificate

Web Files

FON file extension

Generic Font File

Font Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

DEM file extension

Video Game Demo File

Game Files

KML file extension

Keyhole Markup Language File

GIS Files

3GP file extension

3GPP Multimedia File

Video Files

PY file extension

Python Script

Developer Files

GZ file extension

Gnu Zipped Archive

Compressed Files

SYS file extension

Windows System File

System Files