What is a TYPO3 Extension?

TYPO3 consists of a CORE of code which contains the basic functions for managing a database and displaying information from the database. The Core is implemented as an API (an Application Programming Interface) which allows programmers to develop applications which extend the core functionality. It is very much like an operating system - one designed for the management and reporting from a database.

An extension is an application which makes use of the API to provide additional functionality to TYPO3.

As supplied TYPO3 consists of the core code, plus a number of "system" extensions. While a few of these are essential to get TYPO3 to do anything meaningful, the majority, in principle, are not.

The included extensions "just happen" to add up to an extremely powerful web-based content management system.

There is, however, nothing to stop developers from developing quite different applications, with nothing to do with the web, and they would do this by adding alternative extensions.

The vast majority of extensions are, however, about expanding TYPO3's base function as a web based content management system.

Who needs to know this?

Anyone who wants to gain a deeper understanding of how TYPO3 works, and anyone who wants to try installing and using an extension.

You DON'T need to know any of this stuff if you are planning to have your site engineered for you. If that is the case, you only need to know that content elements are all extensions, and how to add them to your page so that you can store and display your content.