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

APK file extension

Android Package File

Executable Files

BAT file extension

DOS Batch File

Executable Files

CER file extension

Internet Security Certificate

Web Files

CUE file extension

Cue Sheet File

Disk Image Files

DNG file extension

Digital Negative Image File

Camera Raw Files

DOC# file extension

Microsoft Word Document

Text Files

DTD file extension

Document Type Definition File

Developer Files

EPUB file extension

Open eBook File

eBook Files

KML file extension

Keyhole Markup Language File

GIS Files

MDF file extension

Media Disc Image File

Disk Image Files

MOBI file extension

Mobipocket eBook

eBook Files

PL file extension

Perl Script

Developer Files

RSS file extension

Rich Site Summary

Web Files

SYS file extension

Windows System File

System Files

3DM file extension

Rhino 3D Model

3D Image Files