petitioner (files a petition asking for a court ruling),
respondent (usually in opposition to a petition or an appeal),
[applicant]] (files an application which may require a ruling on it)
cross-complainant (a defendant who sues someone else in the same lawsuit), or
cross-defendant (a person sued by a cross-complainant).[1]
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.