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

COM file extension

DOS Command File

Executable Files

EPUB file extension

Open eBook File

eBook Files

ICS file extension

iCalendar File

Misc Files

INDD file extension

Adobe InDesign Document

Layout Files

ISO file extension

Disc Image File

Disk Image Files

JS file extension

JavaScript File

Web Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

M file extension

Objective-C Implementation File

Developer Files

MAX file extension

3ds Max Scene File

3D Image Files

MOBI file extension

Mobipocket eBook

eBook Files

MSG file extension

Outlook Mail Message

Text Files

TIF file extension

Tagged Image File

Raster Image Files

TIFF file extension

Tagged Image File Format

Raster Image Files

WMA file extension

Windows Media Audio File

Audio Files

WMV file extension

Windows Media Video File

Video Files