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

ASF file extension

Advanced Systems Format File

Video Files

ASPX file extension

Active Server Page Extended File

Web Files

ASX file extension

Microsoft ASF Redirector File

Video Files

BAK file extension

Backup File

Backup Files

CS file extension

Visual C# Source Code File

Developer Files

DAT file extension

Data File

Data Files

DLL file extension

Dynamic Link Library

System Files

MAX file extension

3ds Max Scene File

3D Image Files

MP3 file extension

MP3 Audio File

Audio Files

RM file extension

Real Media File

Video Files

RTF file extension

Rich Text Format File

Text Files

SYS file extension

Windows System File

System Files

TIFF file extension

Tagged Image File Format

Raster Image Files

WPD file extension

WordPerfect Document

Text Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files