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

ASX file extension

Microsoft ASF Redirector File

Video Files

BAT file extension

DOS Batch File

Executable Files

CRDOWNLOAD file extension

Chrome Partially Downloaded File

Misc Files

CRX file extension

Chrome Extension

Plugin Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

GADGET file extension

Windows Gadget

Executable Files

HTM file extension

Hypertext Markup Language File

Web Files

HTML file extension

Hypertext Markup Language File

Web Files

JAR file extension

Java Archive File

Executable Files

MDF file extension

Media Disc Image File

Disk Image Files

MOBI file extension

Mobipocket eBook

eBook Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

PCT file extension

Picture File

Layout Files

XCODEPROJ file extension

Xcode Project

Developer Files