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

APP file extension

Mac OS X Application

Executable Files

ASPX file extension

Active Server Page Extended File

Web Files

CFG file extension

Configuration File

Settings Files

CFM file extension

ColdFusion Markup File

Web Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

EPUB file extension

Open eBook File

eBook Files

GBR file extension

Gerber File

Data Files

IFF file extension

Interchange File Format

Audio Files

JS file extension

JavaScript File

Web Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

MOBI file extension

Mobipocket eBook

eBook Files

RAR file extension

WinRAR Compressed Archive

Compressed Files

TAX2012 file extension

TurboTax 2012 Tax Return

Data Files

TOAST file extension

Toast Disc Image

Disk Image Files

3G2 file extension

3GPP2 Multimedia File

Video Files