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

CER file extension

Internet Security Certificate

Web Files

CFG file extension

Configuration File

Settings Files

CLASS file extension

Java Class File

Developer Files

CS file extension

Visual C# Source Code File

Developer Files

DOCX file extension

Microsoft Word Open XML Document

Text Files

DWG file extension

AutoCAD Drawing Database File

CAD Files

EPS file extension

Encapsulated PostScript File

Vector Image Files

GAM file extension

Saved Game File

Game Files

ISO file extension

Disc Image File

Disk Image Files

M4A file extension

MPEG-4 Audio File

Audio Files

NES file extension

Nintendo (NES) ROM File

Game Files

RM file extension

Real Media File

Video Files

ROM file extension

N64 Game ROM File

Game Files

RPM file extension

Red Hat Package Manager File

Compressed Files

XLSX file extension

Microsoft Excel Open XML Spreadsheet

Spreadsheet Files