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

AIF file extension

Audio Interchange File Format

Audio Files

ASX file extension

Microsoft ASF Redirector File

Video Files

CER file extension

Internet Security Certificate

Web Files

CS file extension

Visual C# Source Code File

Developer Files

CUR file extension

Windows Cursor

System Files

DLL file extension

Dynamic Link Library

System Files

ICS file extension

iCalendar File

Misc Files

JAR file extension

Java Archive File

Executable Files

JS file extension

JavaScript File

Web Files

MOBI file extension

Mobipocket eBook

eBook Files

RPM file extension

Red Hat Package Manager File

Compressed Files

TAR file extension

Consolidated Unix File Archive

Data Files

TTF file extension

TrueType Font

Font Files

WPD file extension

WordPerfect Document

Text Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files