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

ASP file extension

Active Server Page

Web Files

CER file extension

Internet Security Certificate

Web Files

CSS file extension

Cascading Style Sheet

Web Files

DEM file extension

Video Game Demo File

Game Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

H file extension

C/C++/Objective-C Header File

Developer Files

ICS file extension

iCalendar File

Misc Files

INDD file extension

Adobe InDesign Document

Layout Files

MOBI file extension

Mobipocket eBook

eBook Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

PCT file extension

Picture File

Layout Files

PSPIMAGE file extension

PaintShop Pro Image

Raster Image Files

RA file extension

Real Audio File

Audio Files

RAR file extension

WinRAR Compressed Archive

Compressed Files

RSS file extension

Rich Site Summary

Web Files