Joomla is a free and open-source content management system (CMS) for publishing web content. It is built on a model–view–controller web application framework that can be used independently of the CMS.
Joomla! is written in PHP, uses object-oriented programming (OOP) techniques (since version 1.5) and software design patterns, stores data in a MySQL, MS SQL (since version 2.5), or PostgreSQL (since version 3.0) database, and includes features such as page caching, RSS feeds, printable versions of pages, news flashes, blogs, search, and support for language internationalization.
Like many other web applications, Joomla may be run on a LAMP stack.
Many web hosts have control panels for automatic installation of Joomla. On Windows, Joomla can be installed using the Microsoft Web Platform Installer, which automatically detects and installs dependencies, such as PHP or MySQL. Joomla extensions extend the functionality of Joomla websites. Eight types of extensions may be distinguished: components, modules, plugins, templates, languages, libraries, files and packages. Each of these extensions handles a specific function.COMPONENTS:
Components are the largest and most complex extensions. Most components have two parts: a site part and an administrator part. Every time a Joomla page loads, one component is called to render the main page body. Components produce the major portion of a page because a component is driven by a menu item.PLUGINS:
Plugins are advanced extensions and are, in essence, event handlers. In the execution of any part of Joomla, a module or a component, an event may be triggered. When an event is triggered, plugins that are registered to handle that event execute. For example, a plugin could be used to block user-submitted articles and filter text. The line between plugins and components can sometimes be a little fuzzy. Sometimes large or advanced plugins are called components even though they don't actually render large portions of a page. An SEF URL extension might be created as a component, even though its functionality could be accomplished with just a plugin.TEMPLATES:
Templates describe the main design of a Joomla website. While the CMS manages the website content, templates determine the style or look and feel and layout of a site.MODULES:
Modules is dynamic or static output in an template position. Templates define dynamic positions that can be assigned modules. An example could be a boxed login form in a sidebar. This could be compared to another CMS's "widgets in sidebar". Multiple modules can be assigned to each position and each module's assignment can be controlled per menu item. Historically, modules are assigned to sidebars around the main component output.LANGUAGES:
Languages are very simple extensions that can either be used as a core part or as an extension. Language and font information can also be used for PDF or PSD to Joomla conversions.LIBRARIES:
Libraries are usually extra php libraries that provide functionality for a component, module or plugin to work correctly (such as Google APIs).FILES:
Files are single files that can be installed anywhere in the Joomla file system. Examples of this include allowing extension developers to provide extra template views.PACKAGES:
Packages allow user to install combinations of any other extension type listed above. This allows related packages to be installed and uninstalled in one action rather than as separate entities.