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

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

JAVA file extension

Java Source Code File

Developer Files

DLL file extension

Dynamic Link Library

System Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files

PNG file extension

Portable Network Graphic

Raster Image Files

SYS file extension

Windows System File

System Files

ROM file extension

N64 Game ROM File

Game Files

AIF file extension

Audio Interchange File Format

Audio Files

7Z file extension

7-Zip Compressed File

Compressed Files

PDB file extension

Program Database

Database Files

DTD file extension

Document Type Definition File

Developer Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

HTM file extension

Hypertext Markup Language File

Web Files

M4V file extension

iTunes Video File

Video Files

ICNS file extension

Mac OS X Icon Resource File

System Files