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

IBOOKS file extension

Multi-Touch iBook

Data Files

CLASS file extension

Java Class File

Developer Files

MOBI file extension

Mobipocket eBook

eBook Files

7Z file extension

7-Zip Compressed File

Compressed Files

THM file extension

Thumbnail Image File

Raster Image Files

CPL file extension

Windows Control Panel Item

System Files

ASPX file extension

Active Server Page Extended File

Web Files

NES file extension

Nintendo (NES) ROM File

Game Files

SQL file extension

Structured Query Language Data File

Database Files

FNT file extension

Windows Font File

Font Files

M file extension

Objective-C Implementation File

Developer Files

CAB file extension

Windows Cabinet File

System Files

DOC file extension

Microsoft Word Document

Text Files

C file extension

C/C++ Source Code File

Developer Files

3G2 file extension

3GPP2 Multimedia File

Video Files