The major use of the term content relates to Joomla articles. These items appear in the main part of the page and are managed in the Joomla Administrator under Article Manager. We like to refer to these items as the Primary Content - that is the main content that appears on the page. 

But there are a multitude of potential Secondary Content items that can appear in other parts of the page. Examples include:

Joomla sites can include modules that provide functions such as a form, a login facility, a search box, navigation menus and more. It is arguable whether or not these items fall into the definition of content or not, because they provide function rather than information.

{jb_purplebox}Our free Joomla tutorial course - The Basics - teaches you how to create Joomla content items.{/jb_purplebox}