A party is a person or group of persons that compose a single entity which can be identified as one for the purposes of the law. Parties include: plaintiff (person filing suit), defendant (person sued or charged with a crime), petitioner (files a petition asking for a court ruling), respondent (usually in opposition to a petition or an appeal), cross-complainant (a defendant who sues someone else in the same lawsuit), or 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.
Courts use various terms to identify the role of a particular party in civil litigation, usually identifying the party that brings a lawsuit as the plaintiff, or, in older American cases, the party of the first part; and the party against whom the case was brought as the defendant, or, in older American cases, the party of the second part. In a criminal case in Nigeria and some other countries the parties are called prosecutor and defendant