The designator original is synonymous with this for all notes except alias. In the context of an alias, original is the alias's original note.
This designator is most useful in the context of an agent's action. For instance:
$Container="/Bin";
will move any matching aliases to the root-level note 'Bin' but the query will spawn a new alias next cycle; unless stopped, 'Bin' will fill with aliases as new ones are added each agent cycle. However:
$Container(original)="/Bin";
will move the original not of the alias to 'Bin' causing the original to be out of scope of the agent query and thus having the expected effect.