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

ASPX file extension

Active Server Page Extended File

Web Files

CRDOWNLOAD file extension

Chrome Partially Downloaded File

Misc Files

CSS file extension

Cascading Style Sheet

Web Files

CUE file extension

Cue Sheet File

Disk Image Files

DTD file extension

Document Type Definition File

Developer Files

INDD file extension

Adobe InDesign Document

Layout Files

INI file extension

Windows Initialization File

Settings Files

JS file extension

JavaScript File

Web Files

KMZ file extension

Google Earth Placemark File

GIS Files

PCT file extension

Picture File

Layout Files

PRF file extension

Outlook Profile File

Settings Files

SQL file extension

Structured Query Language Data File

Database Files

TMP file extension

Temporary File

Backup Files

TXT file extension

Plain Text File

Text Files

3G2 file extension

3GPP2 Multimedia File

Video Files