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

DOCX file extension

Microsoft Word Open XML Document

Text Files

MP4 file extension

MPEG-4 Video File

Video Files

SYS file extension

Windows System File

System Files

SITX file extension

StuffIt X Archive

Compressed Files

INI file extension

Windows Initialization File

Settings Files

ZIP file extension

Zipped File

Compressed Files

PDF file extension

Portable Document Format File

Layout Files

COM file extension

DOS Command File

Executable Files

DLL file extension

Dynamic Link Library

System Files

3DS file extension

3D Studio Scene

3D Image Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

CPL file extension

Windows Control Panel Item

System Files

SVG file extension

Scalable Vector Graphics File

Vector Image Files

7Z file extension

7-Zip Compressed File

Compressed Files

OTF file extension

OpenType Font

Font Files