term:

Amicus Curiae

amicus curiae n

pl: amici curiae
[New Latin, literally, friend of the court]
: one (as an individual or organization) that is not a party to a particular lawsuit but is allowed to advise the court regarding a point of law or fact directly concerning the lawsuit [a brief of an amicus curiae may be filed "Federal Rules of Appellate Procedure Rule 29"] called also friend of the court

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.