Hi Dostuff. "Audience targeting" is not yet released. The "Relevant to this user" selection makes it so the person who is logged in and visiting the page see the news in a personalized fashion based on their activities (who they work with and what they work on; aka, a relevant experience based on the intelligence of the Microsoft Graph). Audience targeting will enable a page/news owner to add specific people metadata based on attributes like role, region, title, etc.. from AAD - and "target" that news/page to that type of user - not just what we know about them in the Microsoft Graph. Audience targeting will give content owners a little more control for who sees their content. It is a setting you enable from within the web part, like News or Highlighted Content, that then understands the who as it's programmed into each page, and then does or doesn't show the news/page per the person's AAD information.
Hope that helps. We'll provide richer support information at the time we push the feature into Targeted Release. It is not yet available as of now.
Cheers,
Mark