Content means the information on a site, including text, images, video and other data. In Joomla, com_content identifies the articles component rather than all site content.
What com_content manages
This Joomla core component manages articles and their categories. It supports publication, featured articles, versions, fields and different views. Editors work with articles in the administrator interface, while menu items and component options control public presentation.
Where other content belongs
Contacts, products, third-party directory records and module data may be managed by other Joomla extensions. Their structure, settings and permissions depend on the relevant component. Being displayed on a page does not turn those records into com_content articles.
Distinguish general content from the Joomla articles component to find the correct place to edit each kind of information.