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

COM file extension

DOS Command File

Executable Files

CUR file extension

Windows Cursor

System Files

DNG file extension

Digital Negative Image File

Camera Raw Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

KEY file extension

Keynote Presentation

Data Files

LNK file extension

Windows File Shortcut

System Files

MID file extension

MIDI File

Audio Files

MP3 file extension

MP3 Audio File

Audio Files

MP4 file extension

MPEG-4 Video File

Video Files

MPA file extension

MPEG-2 Audio File

Audio Files

MSG file extension

Outlook Mail Message

Text Files

TIFF file extension

Tagged Image File Format

Raster Image Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files

3DS file extension

3D Studio Scene

3D Image Files