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

BIN file extension

Binary Disc Image

Disk Image Files

CFG file extension

Configuration File

Settings Files

CGI file extension

Common Gateway Interface Script

Executable Files

CSR file extension

Certificate Signing Request File

Web Files

DAT file extension

Data File

Data Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

HTM file extension

Hypertext Markup Language File

Web Files

LUA file extension

Lua Source File

Developer Files

M4A file extension

MPEG-4 Audio File

Audio Files

MAX file extension

3ds Max Scene File

3D Image Files

MSI file extension

Windows Installer Package

Misc Files

PART file extension

Partially Downloaded File

Misc Files

PPTX file extension

PowerPoint Open XML Presentation

Data Files

TXT file extension

Plain Text File

Text Files

XCODEPROJ file extension

Xcode Project

Developer Files