Joomla - a PHP content management system for content-oriented small business sites and communities.
Currently there are three Joomla versions: 1.5, 2.5, and 3.0.
The most important Joomla component allows users to manage and view articles on the site. The articles are grouped in categories. Joomla 1.5 supports two levels of categories: sections on the first level and categories in this sections. Joomla 2.5 supports unlimited levels of categories.
Like other content management systems Joomla allows site owners to customize the site by installing templates (known as themes or skins in other content management systems). The Joomla template specifies layout, available positions, style of modules.
Joomla templates can have parameters (configurable options). Usually they configures text direction (right-to-left or left-to-right), color schema (light, dark, blue, red, etc), header image and other design elements.