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

7Z file extension

7-Zip Compressed File

Compressed Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

CER file extension

Internet Security Certificate

Web Files

DDS file extension

DirectDraw Surface

Raster Image Files

TGA file extension

Targa Graphic

Raster Image Files

ASPX file extension

Active Server Page Extended File

Web Files

PPT file extension

PowerPoint Presentation

Data Files

DEM file extension

Video Game Demo File

Game Files

PAGES file extension

Pages Document

Text Files

SYS file extension

Windows System File

System Files

IBOOKS file extension

Multi-Touch iBook

Data Files

DTD file extension

Document Type Definition File

Developer Files

DLL file extension

Dynamic Link Library

System Files

M4A file extension

MPEG-4 Audio File

Audio Files

XCODEPROJ file extension

Xcode Project

Developer Files