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

BAK file extension

Backup File

Backup Files

BMP file extension

Bitmap Image File

Raster Image Files

CLASS file extension

Java Class File

Developer Files

CPL file extension

Windows Control Panel Item

System Files

DBF file extension

Database File

Database Files

INDD file extension

Adobe InDesign Document

Layout Files

ISO file extension

Disc Image File

Disk Image Files

MAX file extension

3ds Max Scene File

3D Image Files

MDB file extension

Microsoft Access Database

Database Files

NES file extension

Nintendo (NES) ROM File

Game Files

PAGES file extension

Pages Document

Text Files

PNG file extension

Portable Network Graphic

Raster Image Files

SITX file extension

StuffIt X Archive

Compressed Files

TIF file extension

Tagged Image File

Raster Image Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files