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

ZIPX file extension

Extended Zip File

Compressed Files

CPL file extension

Windows Control Panel Item

System Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files

7Z file extension

7-Zip Compressed File

Compressed Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

TAX2012 file extension

TurboTax 2012 Tax Return

Data Files

JAVA file extension

Java Source Code File

Developer Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

PART file extension

Partially Downloaded File

Misc Files

PRF file extension

Outlook Profile File

Settings Files

MOBI file extension

Mobipocket eBook

eBook Files

AZW file extension

Amazon Kindle eBook File

eBook Files

BAK file extension

Backup File

Backup Files

JPG file extension

JPEG Image

Raster Image Files