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

GED file extension

GEDCOM Genealogy Data File

Data Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

CSS file extension

Cascading Style Sheet

Web Files

7Z file extension

7-Zip Compressed File

Compressed Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

BMP file extension

Bitmap Image File

Raster Image Files

ROM file extension

N64 Game ROM File

Game Files

SLN file extension

Visual Studio Solution File

Developer Files

PART file extension

Partially Downloaded File

Misc Files

AZW file extension

Amazon Kindle eBook File

eBook Files

FON file extension

Generic Font File

Font Files

KEY file extension

Keynote Presentation

Data Files

PL file extension

Perl Script

Developer Files

3DM file extension

Rhino 3D Model

3D Image Files

ASPX file extension

Active Server Page Extended File

Web Files