To keep track of which nodes (and other) link to which other ones, the [core] search indexer stores all links in a table called search_node_links. [..I]f you enable the Views module, you can enable a default view called "Backlinks".
The Backlinks view has 2 displays: a block and a page. The block you can put wherever you want, the page is added as an extra tab on each node next to "view" and "edit".
You can also choose to create your own views using the "Search: Links to" and "Search: Links from" argument and filter.