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

CAB file extension

Windows Cabinet File

System Files

DTD file extension

Document Type Definition File

Developer Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

KEYCHAIN file extension

Mac OS X Keychain File

Data Files

M file extension

Objective-C Implementation File

Developer Files

MID file extension

MIDI File

Audio Files

MP3 file extension

MP3 Audio File

Audio Files

OBJ file extension

Wavefront 3D Object File

3D Image Files

PY file extension

Python Script

Developer Files

RM file extension

Real Media File

Video Files

SDF file extension

Standard Data File

Data Files

TTF file extension

TrueType Font

Font Files

WAV file extension

WAVE Audio File

Audio Files

WPD file extension

WordPerfect Document

Text Files