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

RM file extension

Real Media File

Video Files

3G2 file extension

3GPP2 Multimedia File

Video Files

FLA file extension

Adobe Flash Animation

Developer Files

CLASS file extension

Java Class File

Developer Files

VCF file extension

vCard File

Data Files

GED file extension

GEDCOM Genealogy Data File

Data Files

AVI file extension

Audio Video Interleave File

Video Files

M4A file extension

MPEG-4 Audio File

Audio Files

UUE file extension

Uuencoded File

Encoded Files

7Z file extension

7-Zip Compressed File

Compressed Files

INI file extension

Windows Initialization File

Settings Files

JS file extension

JavaScript File

Web Files

CER file extension

Internet Security Certificate

Web Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files