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

MP4 file extension

MPEG-4 Video File

Video Files

JPG file extension

JPEG Image

Raster Image Files

RTF file extension

Rich Text Format File

Text Files

7Z file extension

7-Zip Compressed File

Compressed Files

DLL file extension

Dynamic Link Library

System Files

NES file extension

Nintendo (NES) ROM File

Game Files

PDF file extension

Portable Document Format File

Layout Files

CPP file extension

C++ Source Code File

Developer Files

XML file extension

XML File

Data Files

ASPX file extension

Active Server Page Extended File

Web Files

KEY file extension

Keynote Presentation

Data Files

SDF file extension

Standard Data File

Data Files

VCXPROJ file extension

Visual C++ Project

Developer Files

CAB file extension

Windows Cabinet File

System Files

MOBI file extension

Mobipocket eBook

eBook Files