Template A template is a type of Joomla! extension that changes the way your site looks. There are two types of templates used by the Joomla! CMS: Front-end Templates and Back-end Templates. The Front-end Template controls the way your website is presented to the user viewing the website's content. The Back-end Template controls the way your website's administrative tasks are presented for controlling management functions by a Joomla! Administrator. These would include common tasks such as: user, menu, article, category, module, component, plugin and template management. Reference: http://docs.joomla.org/Glossary
Plugin A plugin is a kind of Joomla! extension. Plugins provide functions which are associated with trigger events. Joomla provides a set of core plugin events, but any extension can fire (custom) events. When a particular event occurs, all plugin functions of the type associated with the event are executed in sequence. This is a powerful way of extending the functionality of the Joomla! Platform. It also offers extension developers a way to allow other extensions to respond to their actions, making extensions extensible. The Joomla! plugin architecture follows the Observer design pattern. The JPlugin class provides the means to register custom plugin code with core or custom events. The JDispatcher class (JEventDispatcher in Joomla 3.x) is an event handler which calls all plugins registered for a particular event, when that event is triggered. Reference: http://docs.joomla.org/Glossary
Template override Template overrides are a way of changing the way Joomla shows something without changing the basic or core Joomla system. A template override is a layout file that is placed in a special subfolder of the template. If found, it will replace the standard layout file for that template.This means that as Joomla is upgraded to new versions you will not have to repeat all the changes you made.
