What  is Content in SharePoint?

Content comprises of documents and list items. Content does not include list or library itself.
List or library helps user to organize the content.
Content is categorized into : structured and unstructured content.
Structured content:
Content which separates storage of its content from its display. e.g. List Items can be sorted/filtered and viewed in List web part or data row in a SQL data table.

Unstructured Content:
Content which cannot be viewed separately the format in which they are stored. e.g. Word document cannot be viewed without the MS Office Word.​