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

CUR file extension

Windows Cursor

System Files

GADGET file extension

Windows Gadget

Executable Files

INDD file extension

Adobe InDesign Document

Layout Files

ISO file extension

Disc Image File

Disk Image Files

MDB file extension

Microsoft Access Database

Database Files

MDF file extension

Media Disc Image File

Disk Image Files

MPG file extension

MPEG Video File

Video Files

PAGES file extension

Pages Document

Text Files

PCT file extension

Picture File

Layout Files

PPS file extension

PowerPoint Slide Show

Data Files

PPTX file extension

PowerPoint Open XML Presentation

Data Files

SITX file extension

StuffIt X Archive

Compressed Files

SYS file extension

Windows System File

System Files

TXT file extension

Plain Text File

Text Files

WSF file extension

Windows Script File

Executable Files