is the purpose of Category headings. It enables you to find all the references to something without knowing where they are.
You can find all references to any page title by clicking on the page title.
This does not work for me, all it does is take me to c2.com 
which is Front Page. -- Jon Grover
You must actually left-click on the title, or right-click and choose "open in new window" which will work as well. But, copy link & paste will not work. The default for empty search is Front Page.
In the case of Category headings, this will find any page included in the category.
Real world examples are Science Citation Index and Fixme Comments.
Which pages may or should contain references to the page of a reverse index?
If a page has the purpose to define a reverse index, then it should be referenced only from such pages which are to be included in this index.
Are there special requirements for the content of pages of reverse indexes?
A page for a reverse index should not have content to which an author could wish to link from a page which shouldn't be included in the reverse index.
A reverse index is the result of a look-up procedure and can have differing scope. In a Personal Wiki with Topical Spaces or Category Spaces, provision for lookup in desired spaces is required for reverse references which exist out of current scope. This may be handled in suitable procedures included in the Wiki Engine. The reverse indexes of this wiki are tied not to the current scope or to references made to the page from external spaces. The lookup apparently is via references from the day before, and do not reflect changes in references made today. --Donald Noyes
Reverse-wise, see Forward Index
See original on c2.com