It's possible to create an invisible link (i.e. a hidden reference) to another page by using the syntax [[|Link], where you do not specify anything in front of the vertical bar. 

For example JMiner has a hidden link to this page. So you will not see a clickable link on the the JMiner page to this page. But notice that JMiner does appear in the "referenced by" section in the left footer area of this page and below (using the ReferringPagesPlugin).

This is most usable as a way to set up keywords (or [categories|]) if you don't want the keywords appearing on the individual pages. You can have a hidden reference to a keyword so that the page will show up on the keyword page (which can also use the [Referring Pages Plugin]) but there is no direct link from the individual pages to a keyword page.