Content elements or applications that are usually displayed in the center of the main content area of a template. This depends on the design of the template in use.
Components are core elements of Joomla!’s functionality. These core elements include Content, Banners, Contact, News Feeds, Polls and Web Links.
Members of the Joomla! community produce third party Joomla! components on a continuous basis.
They are freely available to download from http://extensions.joomla.org/ and a number of other web sites.