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

ASPX file extension

Active Server Page Extended File

Web Files

CER file extension

Internet Security Certificate

Web Files

CPP file extension

C++ Source Code File

Developer Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

ICO file extension

Icon File

System Files

LUA file extension

Lua Source File

Developer Files

M4A file extension

MPEG-4 Audio File

Audio Files

M4V file extension

iTunes Video File

Video Files

MSI file extension

Windows Installer Package

Misc Files

SAV file extension

Saved Game

Game Files

SRT file extension

SubRip Subtitle File

Video Files

TOAST file extension

Toast Disc Image

Disk Image Files

TXT file extension

Plain Text File

Text Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files

3G2 file extension

3GPP2 Multimedia File

Video Files