It refers to the party to the lawsuit who is connected to the case, without any interest or prejudice, so that the court can resolve certain issues or have all the evidence proved with his/her help to give a proper judgement.
n. a defendant or a plaintiff included in a lawsuit because of a technical connection with the matter in dispute, and necessary for the court to decide all issues and make a proper judgment, but with no responsibility, no fault and no right to recovery.
nominal partyOne who is joined as a party or defendant merely because the technical rules of pleading require his presence in the record.
non obstante verdictoNotwithstanding the verdict. A verdict entered by the judge contrary to a jury's verdict.
[Latin nominatus, past participle of nominare to call by name, from nomin- nomen name] in the civil law of Louisiana : having a special or certain name compare innominate
See also: What is the meaning of Party, Issue, Use, Information, Interest?