You may create a category for orphaned or missing pages.
Why should one want to do that?
You may want to prevent orphaned or missing pages being displayed at the root of the wiki tree.
How can you do that?
In your wikiconfig.py file set the wiki_tree_orphaned option to the name of the category you want orphaned or missing pages to be displayed at. For example:
wiki_tree_orphaned = u`CategoryOrphaned`
If you specify the wiki_tree_orphaned option you must also set the name of the root category, as your main categories are moved to the orphaned category. To do this, add the wiki_tree_root option to your wikiconfig.py file. For example:
wiki_tree_root = u`CategoryRoot`
In your main categories, which you want to be displayed at root level, add a reference to the root category.