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

PKG file extension

Mac OS X Installer Package

Compressed Files

DLL file extension

Dynamic Link Library

System Files

VCXPROJ file extension

Visual C++ Project

Developer Files

APK file extension

Android Package File

Executable Files

DMP file extension

Windows Memory Dump

System Files

SLN file extension

Visual Studio Solution File

Developer Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

3DS file extension

3D Studio Scene

3D Image Files

DTD file extension

Document Type Definition File

Developer Files

GIF file extension

Graphical Interchange Format File

Raster Image Files

CPL file extension

Windows Control Panel Item

System Files

7Z file extension

7-Zip Compressed File

Compressed Files

KMZ file extension

Google Earth Placemark File

GIS Files

3GP file extension

3GPP Multimedia File

Video Files