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

CAB file extension

Windows Cabinet File

System Files

COM file extension

DOS Command File

Executable Files

CPP file extension

C++ Source Code File

Developer Files

DNG file extension

Digital Negative Image File

Camera Raw Files

DRV file extension

Device Driver

System Files

DTD file extension

Document Type Definition File

Developer Files

DXF file extension

Drawing Exchange Format File

CAD Files

FLA file extension

Adobe Flash Animation

Developer Files

ICNS file extension

Mac OS X Icon Resource File

System Files

MOBI file extension

Mobipocket eBook

eBook Files

MP3 file extension

MP3 Audio File

Audio Files

MP4 file extension

MPEG-4 Video File

Video Files

PHP file extension

PHP Source Code File

Web Files

SAV file extension

Saved Game

Game Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files