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

AI file extension

Adobe Illustrator File

Vector Image Files

AZW file extension

Amazon Kindle eBook File

eBook Files

CLASS file extension

Java Class File

Developer Files

DAT file extension

Data File

Data Files

DBF file extension

Database File

Database Files

DOC file extension

Microsoft Word Document

Text Files

KEY file extension

Keynote Presentation

Data Files

M4A file extension

MPEG-4 Audio File

Audio Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

OTF file extension

OpenType Font

Font Files

PCT file extension

Picture File

Layout Files

RAR file extension

WinRAR Compressed Archive

Compressed Files

RSS file extension

Rich Site Summary

Web Files

TTF file extension

TrueType Font

Font Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files