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

APP file extension

Mac OS X Application

Executable Files

ASX file extension

Microsoft ASF Redirector File

Video Files

CER file extension

Internet Security Certificate

Web Files

CFG file extension

Configuration File

Settings Files

DLL file extension

Dynamic Link Library

System Files

EPUB file extension

Open eBook File

eBook Files

GZ file extension

Gnu Zipped Archive

Compressed Files

MP3 file extension

MP3 Audio File

Audio Files

OTF file extension

OpenType Font

Font Files

PCT file extension

Picture File

Layout Files

ROM file extension

N64 Game ROM File

Game Files

SDF file extension

Standard Data File

Data Files

SLN file extension

Visual Studio Solution File

Developer Files

YUV file extension

YUV Encoded Image File

Raster Image Files

ZIP file extension

Zipped File

Compressed Files