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

APK file extension

Android Package File

Executable Files

CFG file extension

Configuration File

Settings Files

CGI file extension

Common Gateway Interface Script

Executable Files

CS file extension

Visual C# Source Code File

Developer Files

CUR file extension

Windows Cursor

System Files

DLL file extension

Dynamic Link Library

System Files

IFF file extension

Interchange File Format

Audio Files

KEY file extension

Keynote Presentation

Data Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

M3U file extension

Media Playlist File

Audio Files

MAX file extension

3ds Max Scene File

3D Image Files

SAV file extension

Saved Game

Game Files

SYS file extension

Windows System File

System Files

TTF file extension

TrueType Font

Font Files

3G2 file extension

3GPP2 Multimedia File

Video Files