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

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

CSR file extension

Certificate Signing Request File

Web Files

JPG file extension

JPEG Image

Raster Image Files

NES file extension

Nintendo (NES) ROM File

Game Files

CLASS file extension

Java Class File

Developer Files

INDD file extension

Adobe InDesign Document

Layout Files

DDS file extension

DirectDraw Surface

Raster Image Files

FLA file extension

Adobe Flash Animation

Developer Files

PRF file extension

Outlook Profile File

Settings Files

7Z file extension

7-Zip Compressed File

Compressed Files

CSV file extension

Comma Separated Values File

Data Files

CUR file extension

Windows Cursor

System Files

XCODEPROJ file extension

Xcode Project

Developer Files

CSS file extension

Cascading Style Sheet

Web Files

INI file extension

Windows Initialization File

Settings Files