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

CGI file extension

Common Gateway Interface Script

Executable Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

EXE file extension

Windows Executable File

Executable Files

FNT file extension

Windows Font File

Font Files

H file extension

C/C++/Objective-C Header File

Developer Files

HTML file extension

Hypertext Markup Language File

Web Files

JSP file extension

Java Server Page

Web Files

LNK file extension

Windows File Shortcut

System Files

MDF file extension

Media Disc Image File

Disk Image Files

RSS file extension

Rich Site Summary

Web Files

SYS file extension

Windows System File

System Files

TMP file extension

Temporary File

Backup Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

3DM file extension

Rhino 3D Model

3D Image Files

3DS file extension

3D Studio Scene

3D Image Files