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

CFG file extension

Configuration File

Settings Files

CLASS file extension

Java Class File

Developer Files

CSR file extension

Certificate Signing Request File

Web Files

CUR file extension

Windows Cursor

System Files

EPS file extension

Encapsulated PostScript File

Vector Image Files

EXE file extension

Windows Executable File

Executable Files

HTML file extension

Hypertext Markup Language File

Web Files

ICNS file extension

Mac OS X Icon Resource File

System Files

KMZ file extension

Google Earth Placemark File

GIS Files

M file extension

Objective-C Implementation File

Developer Files

MPA file extension

MPEG-2 Audio File

Audio Files

RTF file extension

Rich Text Format File

Text Files

3GP file extension

3GPP Multimedia File

Video Files