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

ASF file extension

Advanced Systems Format File

Video Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

FNT file extension

Windows Font File

Font Files

H file extension

C/C++/Objective-C Header File

Developer Files

IBOOKS file extension

Multi-Touch iBook

Data Files

JSP file extension

Java Server Page

Web 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

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

MP3 file extension

MP3 Audio File

Audio Files

PCT file extension

Picture File

Layout Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

PPTX file extension

PowerPoint Open XML Presentation

Data Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files