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

CGI file extension

Common Gateway Interface Script

Executable Files

CLASS file extension

Java Class File

Developer Files

DEM file extension

Video Game Demo File

Game Files

DLL file extension

Dynamic Link Library

System Files

GADGET file extension

Windows Gadget

Executable Files

GED file extension

GEDCOM Genealogy Data File

Data Files

JSP file extension

Java Server Page

Web Files

LOG file extension

Log File

Text Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

SWF file extension

Shockwave Flash Movie

Video Files

TARGZ file extension

Compressed Tarball File

Compressed Files

TOAST file extension

Toast Disc Image

Disk Image Files

XCODEPROJ file extension

Xcode Project

Developer Files

XLR file extension

Works Spreadsheet

Spreadsheet Files