The content in Joomla! is the pages of information to be shown on the website.
There are 2 types of content: categorized and uncategorized.

Uncategorized Content:
This refers to plain pages that are shown on the website. You can edit these using the back-end, and add as many of them as you want. These pages do not belong to any category hence they are termed as “uncategorized”.

Categorized Content:
Categorized content also refers to pages, but these pages belong to a structure, which is made up of sections and categories. A section contains different “categories”, which in turn contain pages of content which are also called “content items”.