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

GADGET file extension

Windows Gadget

Executable Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

DAT file extension

Data File

Data Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

3GP file extension

3GPP Multimedia File

Video Files

RTF file extension

Rich Text Format File

Text Files

DOC# file extension

Microsoft Word Document

Text Files

BAK file extension

Backup File

Backup Files

INI file extension

Windows Initialization File

Settings Files

PPTX file extension

PowerPoint Open XML Presentation

Data Files

CLASS file extension

Java Class File

Developer Files

GIF file extension

Graphical Interchange Format File

Raster Image Files

7Z file extension

7-Zip Compressed File

Compressed Files

CPL file extension

Windows Control Panel Item

System Files

MDF file extension

Media Disc Image File

Disk Image Files