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

APP file extension

Mac OS X Application

Executable Files

CER file extension

Internet Security Certificate

Web Files

CSV file extension

Comma Separated Values File

Data Files

DB file extension

Database File

Database Files

DESKTHEMEPACK file extension

Windows 8 Desktop Theme Pack File

System Files

DLL file extension

Dynamic Link Library

System Files

DMP file extension

Windows Memory Dump

System Files

EPUB file extension

Open eBook File

eBook Files

M file extension

Objective-C Implementation File

Developer Files

MDF file extension

Media Disc Image File

Disk Image Files

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

PIF file extension

Program Information File

Executable Files

RM file extension

Real Media File

Video Files

THM file extension

Thumbnail Image File

Raster Image Files

TORRENT file extension

BitTorrent File

Misc Files