Manual:Brokenlinks table

The links and brokenlinks tables have been merged to a single pagelinks table, which records the namespace+title key pair of target links rather than the page ID or the prefixed title.

The brokenlinks table stores links to articles that don't exist yet. This is used for Special:Wantedpages (which is sometimes disabled), and perhaps for some link caching. It is the twin of the links table.

"DESCRIBE brokenlinks" results in this:

bl_from stores the cur_id of the article where the link was put, bl_to stores the name (including namespace prefix) of the desired article.