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

CSS file extension

Cascading Style Sheet

Web Files

DOC# file extension

Microsoft Word Document

Text Files

DTD file extension

Document Type Definition File

Developer Files

IBOOKS file extension

Multi-Touch iBook

Data Files

LUA file extension

Lua Source File

Developer Files

MSI file extension

Windows Installer Package

Misc Files

RM file extension

Real Media File

Video Files

RPM file extension

Red Hat Package Manager File

Compressed Files

RTF file extension

Rich Text Format File

Text Files

SAV file extension

Saved Game

Game Files

SLN file extension

Visual Studio Solution File

Developer Files

TTF file extension

TrueType Font

Font Files

WPS file extension

Microsoft Works Word Processor Document

Text Files

3G2 file extension

3GPP2 Multimedia File

Video Files