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

THM file extension

Thumbnail Image File

Raster Image Files

MDB file extension

Microsoft Access Database

Database Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

INDD file extension

Adobe InDesign Document

Layout Files

MOBI file extension

Mobipocket eBook

eBook Files

KML file extension

Keyhole Markup Language File

GIS Files

WAV file extension

WAVE Audio File

Audio Files

7Z file extension

7-Zip Compressed File

Compressed Files

INI file extension

Windows Initialization File

Settings Files

M4V file extension

iTunes Video File

Video Files

MP4 file extension

MPEG-4 Video File

Video Files

JPG file extension

JPEG Image

Raster Image Files

PPT file extension

PowerPoint Presentation

Data Files

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

ACCDB file extension

Access 2007 Database File

Database Files