1. Reference to a source that supports a statement or is otherwise related to it. In legal documents, the source may be a primary legal authority (such as a case or a statute) or a secondary legal authority (such as a treatise or dictionary).
2. Order from a court or the police commanding one's appearance at a certain time and place. To avoid appearing, one may attempt to show cause for lack of compliance with the order, or sometimes enter a plea and accept judgment by mail (as with a minor traffic violation).