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

AI file extension

Adobe Illustrator File
Vector Image Files

BMP file extension

Bitmap Image File
Raster Image Files

CLASS file extension

Java Class File
Developer Files

CSR file extension

Certificate Signing Request File
Web Files

CUE file extension

Cue Sheet File
Disk Image Files

CUR file extension

Windows Cursor
System Files

DLL file extension

Dynamic Link Library
System Files

JS file extension

JavaScript File
Web Files

M3U file extension

Media Playlist File
Audio Files

MSG file extension

Outlook Mail Message
Text Files

PART file extension

Partially Downloaded File
Misc Files

RA file extension

Real Audio File
Audio Files

THM file extension

Thumbnail Image File
Raster Image Files

TXT file extension

Plain Text File
Text Files

XLS file extension

Excel Spreadsheet
Spreadsheet Files