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

CAB file extension

Windows Cabinet File

System Files

EXE file extension

Windows Executable File

Executable Files

HTM file extension

Hypertext Markup Language File

Web Files

ICO file extension

Icon File

System Files

LUA file extension

Lua Source File

Developer Files

M4V file extension

iTunes Video File

Video Files

MSG file extension

Outlook Mail Message

Text Files

PCT file extension

Picture File

Layout Files

PDF file extension

Portable Document Format File

Layout Files

PHP file extension

PHP Source Code File

Web Files

PSD file extension

Adobe Photoshop Document

Raster Image Files

SITX file extension

StuffIt X Archive

Compressed Files

TOAST file extension

Toast Disc Image

Disk Image Files

WPS file extension

Microsoft Works Word Processor Document

Text Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files