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

CFG file extension

Configuration File

Settings Files

CGI file extension

Common Gateway Interface Script

Executable Files

DDS file extension

DirectDraw Surface

Raster Image Files

DTD file extension

Document Type Definition File

Developer Files

EPS file extension

Encapsulated PostScript File

Vector Image Files

GED file extension

GEDCOM Genealogy Data File

Data Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

ICNS file extension

Mac OS X Icon Resource File

System Files

MAX file extension

3ds Max Scene File

3D Image Files

MOBI file extension

Mobipocket eBook

eBook Files

MP4 file extension

MPEG-4 Video File

Video Files

PCT file extension

Picture File

Layout Files

PS file extension

PostScript File

Vector Image Files

SWF file extension

Shockwave Flash Movie

Video Files

TTF file extension

TrueType Font

Font Files