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

APP file extension

Mac OS X Application

Executable Files

TMP file extension

Temporary File

Backup Files

7Z file extension

7-Zip Compressed File

Compressed Files

KML file extension

Keyhole Markup Language File

GIS Files

THM file extension

Thumbnail Image File

Raster Image Files

CPL file extension

Windows Control Panel Item

System Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

3DM file extension

Rhino 3D Model

3D Image Files

MDB file extension

Microsoft Access Database

Database Files

DOC file extension

Microsoft Word Document

Text Files

DOC# file extension

Microsoft Word Document

Text Files

PKG file extension

Mac OS X Installer Package

Compressed Files

ASP file extension

Active Server Page

Web Files

CRX file extension

Chrome Extension

Plugin Files

WAV file extension

WAVE Audio File

Audio Files