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

ASP file extension

Active Server Page

Web Files

CER file extension

Internet Security Certificate

Web Files

CPP file extension

C++ Source Code File

Developer Files

CSV file extension

Comma Separated Values File

Data Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

HTM file extension

Hypertext Markup Language File

Web Files

JAVA file extension

Java Source Code File

Developer Files

MDF file extension

Media Disc Image File

Disk Image Files

MID file extension

MIDI File

Audio Files

PRF file extension

Outlook Profile File

Settings Files

SH file extension

Bash Shell Script

Developer Files

SWF file extension

Shockwave Flash Movie

Video Files

SYS file extension

Windows System File

System Files

TAX2012 file extension

TurboTax 2012 Tax Return

Data Files

WMA file extension

Windows Media Audio File

Audio Files