Missing Page
The link you clicked belongs to a page that hasn't been created yet. It would be a different color from a normal link, and usually this means that someone put a placeholder wikilink somewhere. Like this:
[[focus-panel]][[focus-panel|FocusPanel]][[focus-panels]][[focus-panels|Focus Panels]]
Notice above that the first version doesn't exist (because the page we want is actually the second one; this is to show you what these links appear like in real time.)
Notes
Note that this differs from a regular 404 page (you can see ours there). If you try to visit a page directly that doesn't exist, you will end up with a 404 missing page error. These specific missing page links only appear if you use a wikilink that points to a page that doesn't exist.