From Boldcore's wiki
This page lists tracking categories which are automatically populated by the MediaWiki software. Their names can be changed by altering the relevant system messages in the MediaWiki namespace.
| Tracking category | Message name | Category inclusion criteria |
|---|---|---|
| Indexed pages | index-category | The page has a __INDEX__ on it (and is in a namespace where that flag is allowed), and hence is indexed by robots where it normally wouldn't be. |
| Noindexed pages | noindex-category | The page is not indexed by robots because it has the magic word __NOINDEX__ on it and is in a namespace where that flag is allowed. |
| Pages with too many expensive parser function calls | expensive-parserfunction-category | Too many expensive parser functions (like #ifexist) included on a page. See Manual:$wgExpensiveParserFunctionLimit. |
| Pages containing omitted template arguments | post-expand-template-argument-category | After expanding a template argument (something in triple braces, like {{{Foo}}}), the page is bigger than $wgMaxArticleSize. |
| Pages where template include size is exceeded | post-expand-template-inclusion-category | After expanding all the templates, the page size is bigger than $wgMaxArticleSize, so some templates weren't expanded. |
| Hidden categories | hidden-category-category | This is a category with __HIDDENCAT__ on it, which prevents it from showing up in the category links box on pages, by default. |
| Pages with broken file links | broken-file-category | Category added if the page contains a broken file link (a link to embed a file when the file does not exist). |