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

PPTX file extension

PowerPoint Open XML Presentation

Data Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

7Z file extension

7-Zip Compressed File

Compressed Files

M4A file extension

MPEG-4 Audio File

Audio Files

RA file extension

Real Audio File

Audio Files

TIFF file extension

Tagged Image File Format

Raster Image Files

C file extension

C/C++ Source Code File

Developer Files

OTF file extension

OpenType Font

Font Files

GAM file extension

Saved Game File

Game Files

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

M file extension

Objective-C Implementation File

Developer Files

SAV file extension

Saved Game

Game Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

CLASS file extension

Java Class File

Developer Files

CSS file extension

Cascading Style Sheet

Web Files