A party is a person or group of persons that make up a single for the purposes of the law. They are a participant in legal proceeding and have an interest in the outcome. Parties include: the plaintiff, the defendant, a petitioner or a respondent. They can also be a cross-complainant (a defendant who sues someone else in the same lawsuit) or a cross-defendant (a person sued by a cross-complainant). A person who only appears in the case as a witness is not considered a party.