Plugins
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. Help
Search
The search component uses plugins to control which parts of your Joomla! site are searched. You may choose to turn off some areas to improve performance or for other reasons. Many third party Joomla! extensions have search plugins that extend where search takes place.
Default On:
System
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 is the redirect plugin that together with the redirect component will assist you in managing changes in URLs.
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Default off: