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

AI file extension

Adobe Illustrator File

Vector Image Files

APP file extension

Mac OS X Application

Executable Files

BAK file extension

Backup File

Backup Files

CER file extension

Internet Security Certificate

Web Files

CSS file extension

Cascading Style Sheet

Web Files

DXF file extension

Drawing Exchange Format File

CAD Files

GED file extension

GEDCOM Genealogy Data File

Data Files

INDD file extension

Adobe InDesign Document

Layout Files

KMZ file extension

Google Earth Placemark File

GIS Files

MID file extension

MIDI File

Audio Files

PIF file extension

Program Information File

Executable Files

SITX file extension

StuffIt X Archive

Compressed Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files

3DM file extension

Rhino 3D Model

3D Image Files