"Friend of the court" is a legal term that describes a person or organization who is not a party to a lawsuit but provides assistance or expert opinion to the court. There are several synonyms for this term such as amicus curiae, third-party intervenor, or public interest litigator. Amicus curiae is a Latin term that literally means 'friend of the court' and is the most commonly used synonym. Third-party intervenor refers to a party who intervenes in an ongoing lawsuit, taking the side of one of the parties. Public interest litigator is a person or organization who takes legal action to promote the public interest, and their opinions can be valuable to the court.