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

CER file extension

Internet Security Certificate

Web Files

CFG file extension

Configuration File

Settings Files

DEB file extension

Debian Software Package

Compressed Files

DLL file extension

Dynamic Link Library

System Files

EXE file extension

Windows Executable File

Executable Files

HTML file extension

Hypertext Markup Language File

Web Files

ICNS file extension

Mac OS X Icon Resource File

System Files

MSG file extension

Outlook Mail Message

Text Files

PDF file extension

Portable Document Format File

Layout Files

PLUGIN file extension

Mac OS X Plug-in

Plugin Files

RTF file extension

Rich Text Format File

Text Files

SQL file extension

Structured Query Language Data File

Database Files

UUE file extension

Uuencoded File

Encoded Files

VB file extension

VBScript File

Executable Files

XML file extension

XML File

Data Files