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

TAR file extension

Consolidated Unix File Archive

Data Files

7Z file extension

7-Zip Compressed File

Compressed Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

LOG file extension

Log File

Text Files

M3U file extension

Media Playlist File

Audio Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

MID file extension

MIDI File

Audio Files

ICNS file extension

Mac OS X Icon Resource File

System Files

MDF file extension

Media Disc Image File

Disk Image Files

M4A file extension

MPEG-4 Audio File

Audio Files

SYS file extension

Windows System File

System Files

DLL file extension

Dynamic Link Library

System Files

GAM file extension

Saved Game File

Game Files

MDB file extension

Microsoft Access Database

Database Files