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

AZW file extension

Amazon Kindle eBook File

eBook Files

CUR file extension

Windows Cursor

System Files

DEM file extension

Video Game Demo File

Game Files

DLL file extension

Dynamic Link Library

System Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

DTD file extension

Document Type Definition File

Developer Files

HTM file extension

Hypertext Markup Language File

Web Files

JAVA file extension

Java Source Code File

Developer Files

M4V file extension

iTunes Video File

Video Files

PKG file extension

Mac OS X Installer Package

Compressed Files

PSD file extension

Adobe Photoshop Document

Raster Image Files

SAV file extension

Saved Game

Game Files

SYS file extension

Windows System File

System Files

XML file extension

XML File

Data Files

ZIPX file extension

Extended Zip File

Compressed Files