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

CSR file extension

Certificate Signing Request File

Web Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

FNT file extension

Windows Font File

Font Files

GAM file extension

Saved Game File

Game Files

HTM file extension

Hypertext Markup Language File

Web Files

ISO file extension

Disc Image File

Disk Image Files

M file extension

Objective-C Implementation File

Developer Files

NES file extension

Nintendo (NES) ROM File

Game Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

PPTX file extension

PowerPoint Open XML Presentation

Data Files

RM file extension

Real Media File

Video Files

SITX file extension

StuffIt X Archive

Compressed Files

TAX2012 file extension

TurboTax 2012 Tax Return

Data Files

TOAST file extension

Toast Disc Image

Disk Image Files

XLR file extension

Works Spreadsheet

Spreadsheet Files