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

APP file extension

Mac OS X Application

Executable Files

BAK file extension

Backup File

Backup Files

CGI file extension

Common Gateway Interface Script

Executable Files

CPL file extension

Windows Control Panel Item

System Files

EPUB file extension

Open eBook File

eBook Files

ICNS file extension

Mac OS X Icon Resource File

System Files

INDD file extension

Adobe InDesign Document

Layout Files

LUA file extension

Lua Source File

Developer Files

MDF file extension

Media Disc Image File

Disk Image Files

MP3 file extension

MP3 Audio File

Audio Files

ODT file extension

OpenDocument Text Document

Text Files

PPTX file extension

PowerPoint Open XML Presentation

Data Files

SDF file extension

Standard Data File

Data Files

3DM file extension

Rhino 3D Model

3D Image Files