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

ACCDB file extension

Access 2007 Database File

Database Files

CPP file extension

C++ Source Code File

Developer Files

CSS file extension

Cascading Style Sheet

Web Files

EPUB file extension

Open eBook File

eBook Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

LOG file extension

Log File

Text Files

M3U file extension

Media Playlist File

Audio Files

MAX file extension

3ds Max Scene File

3D Image Files

MOBI file extension

Mobipocket eBook

eBook Files

MSG file extension

Outlook Mail Message

Text Files

ODT file extension

OpenDocument Text Document

Text Files

RA file extension

Real Audio File

Audio Files

TMP file extension

Temporary File

Backup Files

TXT file extension

Plain Text File

Text Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files