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

C file extension

C/C++ Source Code File

Developer Files

CLASS file extension

Java Class File

Developer Files

CPL file extension

Windows Control Panel Item

System Files

CUE file extension

Cue Sheet File

Disk Image Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

GADGET file extension

Windows Gadget

Executable Files

M3U file extension

Media Playlist File

Audio Files

MDF file extension

Media Disc Image File

Disk Image Files

MOV file extension

Apple QuickTime Movie

Video Files

PDF file extension

Portable Document Format File

Layout Files

RTF file extension

Rich Text Format File

Text Files

SITX file extension

StuffIt X Archive

Compressed Files

SQL file extension

Structured Query Language Data File

Database Files

UUE file extension

Uuencoded File

Encoded Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files