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

DAT file extension

Data File

Data Files

DLL file extension

Dynamic Link Library

System Files

FLV file extension

Flash Video File

Video Files

GAM file extension

Saved Game File

Game Files

ICNS file extension

Mac OS X Icon Resource File

System Files

JS file extension

JavaScript File

Web Files

M file extension

Objective-C Implementation File

Developer Files

MOBI file extension

Mobipocket eBook

eBook Files

PDF file extension

Portable Document Format File

Layout Files

PPS file extension

PowerPoint Slide Show

Data Files

PSD file extension

Adobe Photoshop Document

Raster Image Files

SVG file extension

Scalable Vector Graphics File

Vector Image Files

WPD file extension

WordPerfect Document

Text Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files