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

DEM file extension

Video Game Demo File

Game Files

DMG file extension

Mac OS X Disk Image

Disk Image Files

H file extension

C/C++/Objective-C Header File

Developer Files

ICNS file extension

Mac OS X Icon Resource File

System Files

ISO file extension

Disc Image File

Disk Image Files

JAVA file extension

Java Source Code File

Developer Files

MDB file extension

Microsoft Access Database

Database Files

PAGES file extension

Pages Document

Text Files

PY file extension

Python Script

Developer Files

RPM file extension

Red Hat Package Manager File

Compressed Files

SQL file extension

Structured Query Language Data File

Database Files

UUE file extension

Uuencoded File

Encoded Files

VOB file extension

DVD Video Object File

Video Files

XCODEPROJ file extension

Xcode Project

Developer Files