Manual:$wgTrackingCategories

Details
$wgTrackingCategories is the list of tracking categories which are automatically added to pages. They are listed on Special:TrackingCategories.

People who write extensions that add tracking categories via  should add the system message corresponding to their tracking category to this array. They should also define a message with the same name but -desc appended that describes the criteria for a page to be tagged with the tracking category.