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

COM file extension

DOS Command File

Executable Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

DLL file extension

Dynamic Link Library

System Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

GPX file extension

GPS Exchange File

GIS Files

MSG file extension

Outlook Mail Message

Text Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

PNG file extension

Portable Network Graphic

Raster Image Files

PY file extension

Python Script

Developer Files

SDF file extension

Standard Data File

Data Files

SWF file extension

Shockwave Flash Movie

Video Files

TMP file extension

Temporary File

Backup Files

VCXPROJ file extension

Visual C++ Project

Developer Files

XLR file extension

Works Spreadsheet

Spreadsheet Files

3G2 file extension

3GPP2 Multimedia File

Video Files