System plugins operate every time a page on your site loads. They control such things as your URLS, whether users can check a "remember me" box on the login module, and whether caching is enabled. New in 1.6 is the redirect plugin that with the redirect component assist you in managing changes in URLs.
Default on:
- Remember me Help
- SEFHelp
- DebugHelp
Default off:
- CacheHelp
- LogHelp
- RedirectHelp
Default on:
- Joomla Help
Default off:
Two new plugins are available in 1.6 but are disabled by default.
- Contact CreatorHelp
Creates a new linked contact record for each new user created. - ProfileHelp
This example profile plugin allows you to insert additional fields into user registration and profile display. This is intended as an example of the types of extensions to the profile you might want to create.
Content plugins run when specific kinds of pages are loaded. They do things ranging from protecting email addresses from harvesters to creating page breaks.
Default on:
- Email Cloaking Help
- Load Module Help
- Page Break Help
- Page Navigation Help
- Rating Help
Default off:
- Code Highlighting (Geshi) Help
Subcategories
Components
Components are larger extensions that produce the major content for your site. Each component has one or more "views" that control how content is displayed.In the Joomla! administrator there are additional extensions suce as Menus, Redirection, and the extension managers.
Modules
Modules are small blocks of content that can be displayed in positions on a web page. The menus on this site are displayed in modules. The core of Joomla! includes 17 separate modules ranging from login to search to random images. Each module has a name that starts mod_ but when it displays it has a title. In the descriptions in this section, the titles are the same as the names.
Plugins are small task oriented extensions that enhance the Joomla! framework. Some are associated with particular extensions and others, such as editors, are used across all of Joomla!. Most beginning users do not need to change any of the plugins that install with Joomla!. 
