Hi Kris,
It's just abbreviation of the package name. Typically you can see from the class description full name of the package ... example:
actrl:AuxRule (Access Control Auxillary Rule)
I'm not aware if there is document with the list of package abbreviations and it's full description of each of them, but I suppose class name and description should give ample info to understand it's meaning or scope.
Hope you'll find provided information helpful.
Kind regards,
Mio