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

CAB file extension

Windows Cabinet File

System Files

CSS file extension

Cascading Style Sheet

Web Files

DAT file extension

Data File

Data Files

DBF file extension

Database File

Database Files

HTML file extension

Hypertext Markup Language File

Web Files

ICS file extension

iCalendar File

Misc Files

M file extension

Objective-C Implementation File

Developer Files

MDF file extension

Media Disc Image File

Disk Image Files

OTF file extension

OpenType Font

Font Files

PHP file extension

PHP Source Code File

Web Files

SLN file extension

Visual Studio Solution File

Developer Files

SYS file extension

Windows System File

System Files

TOAST file extension

Toast Disc Image

Disk Image Files

WAV file extension

WAVE Audio File

Audio Files

3DS file extension

3D Studio Scene

3D Image Files