The (CMS) software manages content (text, graphics, links, etc.) for distribution on a web server. Usually the software provides tools where users with little or no knowledge of programming languages and markup languages (such as HTML) can create and manage content with relative ease of use.
From Wikipedia

A (Web) Content Management System or CMS in short, allows for easy management of all your website content without worrying about how it will be displayed on the site. This means that editing, replacing and adding content is done through some kind of administrative interface and the delivery and presentation of that content is left up to the system allowing content contributors to focus on their task. All the content is usually stored in a database.
The design and layout of the site is defined by templates. Templates define the way your site will look to your visitors. The benefit of this is if you want to change the look of your website you can just change the template and immediately all the pages on your site will use the new look. The template simply contains the general layout, style and instructions for displaying your content.
Joomla! is such a CMS. It is built using the PHP programming language and the MySQL database server. Both technologies ensure that you will be able to host your Joomla! site almost on any web hosting service. All that is necessary for your Joomla! website is a server with PHP and a MySQL database.

Open Source Software

The basic idea behind open source is very simple: When programmers can read, redistribute, and modify the source code for a piece of software, the software evolves. People improve it, people adapt it, people fix bugs. And this can happen at a speed that, if one is used to the slow pace of conventional software development, seems astonishing.

People often wonder about the quality, reliability and support of Open Source software. It is true that some projects are indeed three day wonders and then they die as the developers move on to something else.
There are also very successful projects with dedicated developers and efficient management. Joomla! is one of those projects. It has been active ever since it's inception, releases are regular and bugs are fixed promptly. A lot of work is being done on improving the code and creating a system that is powerful, yet easy to use and extend. The Joomla! developers have published a detailed road-map outlining the future development direction of the project.
Joomla! has a large user community supported by the high traffic forums. There are numerous websites with news, articles, tips, extensions and templates for Joomla!. The number of websites built using Joomla! is steadily growing with larger organisations adopting Joomla! as their solution of choice.
These are only some highlights and reasons why we at 3point3 have chosen to use Joomla! as the base of our packages. We believe that this software system enables us to provide our customers with professional, reliable and high quality solutions whilst keeping a manageable learning curve. The modular structure of Joomla! allows for incremental building of a website where we can set up the base system and then add and customise new features as required. We have developed a range of packages that already integrate the basic Joomla! software with a number of extra extensions.

Let's get onto the Joomla! features.