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.

What is a Joomla component?

A component is a kind of Joomla! extension. Components are the main functional units of Joomla!; they can be seen as mini-applications. Joomla! comes with a number of core components, like the content management system, contact forms and Web Links.