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

DDS file extension

DirectDraw Surface

Raster Image Files

DEB file extension

Debian Software Package

Compressed Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

HQX file extension

BinHex 4.0 Encoded File

Encoded Files

ICNS file extension

Mac OS X Icon Resource File

System Files

JAR file extension

Java Archive File

Executable Files

KEY file extension

Keynote Presentation

Data Files

MSG file extension

Outlook Mail Message

Text Files

OTF file extension

OpenType Font

Font Files

RSS file extension

Rich Site Summary

Web Files

SH file extension

Bash Shell Script

Developer Files

SQL file extension

Structured Query Language Data File

Database Files

SWF file extension

Shockwave Flash Movie

Video Files

THM file extension

Thumbnail Image File

Raster Image Files

TIF file extension

Tagged Image File

Raster Image Files