Structured vs unstructured content
Structured content is basically the content model in MVC. Use structured content when you have data that can be expressed as a discrete set of fields. These fields make it easier for content editors to enter content reliably. They also allow developers to digest the content more easily and reuse it throughout the web site.
Use unstructured content when the data cannot be expressed as a discrete set of fields. This kind of content is generally entered as formatted text in a rich text field either in a field on a page type or in the page tab as content of a text editing widget.