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

ASF file extension

Advanced Systems Format File

Video Files

CSV file extension

Comma Separated Values File

Data Files

DEM file extension

Video Game Demo File

Game Files

GZ file extension

Gnu Zipped Archive

Compressed Files

HTML file extension

Hypertext Markup Language File

Web Files

MP3 file extension

MP3 Audio File

Audio Files

MP4 file extension

MPEG-4 Video File

Video Files

OTF file extension

OpenType Font

Font Files

PDF file extension

Portable Document Format File

Layout Files

PSD file extension

Adobe Photoshop Document

Raster Image Files

RSS file extension

Rich Site Summary

Web Files

SWF file extension

Shockwave Flash Movie

Video Files

THM file extension

Thumbnail Image File

Raster Image Files

TIFF file extension

Tagged Image File Format

Raster Image Files

TOAST file extension

Toast Disc Image

Disk Image Files