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

7Z file extension

7-Zip Compressed File

Compressed Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

DNG file extension

Digital Negative Image File

Camera Raw Files

COM file extension

DOS Command File

Executable Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

ICNS file extension

Mac OS X Icon Resource File

System Files

AZW file extension

Amazon Kindle eBook File

eBook Files

IBOOKS file extension

Multi-Touch iBook

Data Files

ICO file extension

Icon File

System Files

H file extension

C/C++/Objective-C Header File

Developer Files

CGI file extension

Common Gateway Interface Script

Executable Files

TTF file extension

TrueType Font

Font Files

DLL file extension

Dynamic Link Library

System Files

CAB file extension

Windows Cabinet File

System Files

DMP file extension

Windows Memory Dump

System Files