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

CGI file extension

Common Gateway Interface Script

Executable Files

DOC file extension

Microsoft Word Document

Text Files

GADGET file extension

Windows Gadget

Executable Files

GAM file extension

Saved Game File

Game Files

IFF file extension

Interchange File Format

Audio Files

INDD file extension

Adobe InDesign Document

Layout Files

JSP file extension

Java Server Page

Web Files

MDF file extension

Media Disc Image File

Disk Image Files

PCT file extension

Picture File

Layout Files

PDB file extension

Program Database

Database Files

PKG file extension

Mac OS X Installer Package

Compressed Files

PPT file extension

PowerPoint Presentation

Data Files

SAV file extension

Saved Game

Game Files

SYS file extension

Windows System File

System Files

3DM file extension

Rhino 3D Model

3D Image Files