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

CAB file extension

Windows Cabinet File

System Files

CER file extension

Internet Security Certificate

Web Files

CFM file extension

ColdFusion Markup File

Web Files

CRX file extension

Chrome Extension

Plugin Files

DAT file extension

Data File

Data Files

DNG file extension

Digital Negative Image File

Camera Raw Files

DTD file extension

Document Type Definition File

Developer Files

M4A file extension

MPEG-4 Audio File

Audio Files

MPG file extension

MPEG Video File

Video Files

OTF file extension

OpenType Font

Font Files

ROM file extension

N64 Game ROM File

Game Files

SDF file extension

Standard Data File

Data Files

SWF file extension

Shockwave Flash Movie

Video Files

XLR file extension

Works Spreadsheet

Spreadsheet Files