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

AI file extension

Adobe Illustrator File

Vector Image Files

APP file extension

Mac OS X Application

Executable Files

BMP file extension

Bitmap Image File

Raster Image Files

CAB file extension

Windows Cabinet File

System Files

DTD file extension

Document Type Definition File

Developer Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

INI file extension

Windows Initialization File

Settings Files

KMZ file extension

Google Earth Placemark File

GIS Files

MPG file extension

MPEG Video File

Video Files

NES file extension

Nintendo (NES) ROM File

Game Files

OTF file extension

OpenType Font

Font Files

PKG file extension

Mac OS X Installer Package

Compressed Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

SVG file extension

Scalable Vector Graphics File

Vector Image Files

THM file extension

Thumbnail Image File

Raster Image Files