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

AIF file extension

Audio Interchange File Format

Audio Files

CAB file extension

Windows Cabinet File

System Files

CGI file extension

Common Gateway Interface Script

Executable Files

CLASS file extension

Java Class File

Developer Files

CSS file extension

Cascading Style Sheet

Web Files

CUR file extension

Windows Cursor

System Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

GED file extension

GEDCOM Genealogy Data File

Data Files

INDD file extension

Adobe InDesign Document

Layout Files

M4V file extension

iTunes Video File

Video Files

MOBI file extension

Mobipocket eBook

eBook Files

PPT file extension

PowerPoint Presentation

Data Files

SH file extension

Bash Shell Script

Developer Files

XLR file extension

Works Spreadsheet

Spreadsheet Files

3G2 file extension

3GPP2 Multimedia File

Video Files