A content notification is a link to a notification page. This notification page lists the backlinks to itself.
A web page can link to other pages, e.g. pageA contains a link to pageB. A backlink traces the link backwards. Thus for the link from pageA to pageB, pageA is listed as a backlink to pageB. By including a link to a "collection page" it is possible to embed a notification in the page content.
Below is an image of the "Pending" page. Other wiki pages, which are not complete can include a link to the Pending page and get listed there.
The member page has a Backlinks tab with some built-in notification pages. The "Pending" list is one of them. It is possible to define other such pages to capture content notifications