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

APP file extension

Mac OS X Application

Executable Files

DOC file extension

Microsoft Word Document

Text Files

SLN file extension

Visual Studio Solution File

Developer Files

INDD file extension

Adobe InDesign Document

Layout Files

ZIP file extension

Zipped File

Compressed Files

RTF file extension

Rich Text Format File

Text Files

DLL file extension

Dynamic Link Library

System Files

VCD file extension

Virtual CD

Disk Image Files

LNK file extension

Windows File Shortcut

System Files

M4A file extension

MPEG-4 Audio File

Audio Files

C file extension

C/C++ Source Code File

Developer Files

7Z file extension

7-Zip Compressed File

Compressed Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

DOC# file extension

Microsoft Word Document

Text Files

3GP file extension

3GPP Multimedia File

Video Files