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

CSR file extension

Certificate Signing Request File

Web Files

EPUB file extension

Open eBook File

eBook Files

EXE file extension

Windows Executable File

Executable Files

ICNS file extension

Mac OS X Icon Resource File

System Files

MIM file extension

Multi-Purpose Internet Mail Message File

Encoded Files

MOBI file extension

Mobipocket eBook

eBook Files

PAGES file extension

Pages Document

Text Files

PDB file extension

Program Database

Database Files

PSD file extension

Adobe Photoshop Document

Raster Image Files

RSS file extension

Rich Site Summary

Web Files

SRT file extension

SubRip Subtitle File

Video Files

TMP file extension

Temporary File

Backup Files

WPD file extension

WordPerfect Document

Text Files

XHTML file extension

Extensible Hypertext Markup Language File

Web Files

3DS file extension

3D Studio Scene

3D Image Files