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

SITX file extension

StuffIt X Archive

Compressed Files

CSV file extension

Comma Separated Values File

Data Files

GZ file extension

Gnu Zipped Archive

Compressed Files

FLV file extension

Flash Video File

Video Files

3GP file extension

3GPP Multimedia File

Video Files

ASPX file extension

Active Server Page Extended File

Web Files

ZIP file extension

Zipped File

Compressed Files

ICNS file extension

Mac OS X Icon Resource File

System Files

7Z file extension

7-Zip Compressed File

Compressed Files

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

NES file extension

Nintendo (NES) ROM File

Game Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

BAK file extension

Backup File

Backup Files

XLS file extension

Excel Spreadsheet

Spreadsheet Files

IFF file extension

Interchange File Format

Audio Files