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

ASPX file extension

Active Server Page Extended File

Web Files

CSS file extension

Cascading Style Sheet

Web Files

DLL file extension

Dynamic Link Library

System Files

KML file extension

Keyhole Markup Language File

GIS Files

M3U file extension

Media Playlist File

Audio Files

MOV file extension

Apple QuickTime Movie

Video Files

MP3 file extension

MP3 Audio File

Audio Files

MSG file extension

Outlook Mail Message

Text Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

PCT file extension

Picture File

Layout Files

PDB file extension

Program Database

Database Files

PHP file extension

PHP Source Code File

Web Files

RPM file extension

Red Hat Package Manager File

Compressed Files

TOAST file extension

Toast Disc Image

Disk Image Files

ZIPX file extension

Extended Zip File

Compressed Files