Plug in Concept

Joomla's Plug-in's hook into the system core and components and sometime content.



An example is the load modules Plug-in it loads a module position name into an article and then renders the module or modules assigned
to that module position name.

By adding this type of tag "{loadposition left}". loads the module position left if the module is active.
Then renders the module in the content.

This is just one type of Joomla Plug-in there others but your starting to see the power of Joomla's extensions.