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

CSS file extension

Cascading Style Sheet

Web Files

CSV file extension

Comma Separated Values File

Data Files

HTM file extension

Hypertext Markup Language File

Web Files

ICO file extension

Icon File

System Files

INDD file extension

Adobe InDesign Document

Layout Files

MOV file extension

Apple QuickTime Movie

Video Files

MPA file extension

MPEG-2 Audio File

Audio Files

MSI file extension

Windows Installer Package

Misc Files

PKG file extension

Mac OS X Installer Package

Compressed Files

PL file extension

Perl Script

Developer Files

RA file extension

Real Audio File

Audio Files

ROM file extension

N64 Game ROM File

Game Files

SLN file extension

Visual Studio Solution File

Developer Files

SRT file extension

SubRip Subtitle File

Video Files

ZIP file extension

Zipped File

Compressed Files