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

BMP file extension

Bitmap Image File

Raster Image Files

DEM file extension

Video Game Demo File

Game Files

JAR file extension

Java Archive File

Executable Files

MDB file extension

Microsoft Access Database

Database Files

MP3 file extension

MP3 Audio File

Audio Files

PCT file extension

Picture File

Layout Files

PHP file extension

PHP Source Code File

Web Files

PKG file extension

Mac OS X Installer Package

Compressed Files

PSD file extension

Adobe Photoshop Document

Raster Image Files

SYS file extension

Windows System File

System Files

TAX2012 file extension

TurboTax 2012 Tax Return

Data Files

VOB file extension

DVD Video Object File

Video Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

3GP file extension

3GPP Multimedia File

Video Files