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
These plugins are the buttons found beneath your editor. They only run when an editor plugin runs.
Content plugins run when specific kinds of pages are loaded. They do things ranging from protecting email addresses from harvesters to creating page breaks.