A more thorough explanation:

An amicus brief is a legal document prepared by a third party, known as an amicus curiae, who is not directly involved in a lawsuit but has an interest in the outcome. The brief is submitted to the court with the permission of the judge and provides additional information or arguments that may be helpful in deciding the case.

For example, a civil rights organization may file an amicus brief in a case involving discrimination to provide the court with information about the impact of the decision on minority communities. Similarly, a group of scientists may file an amicus brief in a case involving environmental regulations to provide the court with scientific evidence about the potential harm to the environment.

Amicus briefs are commonly filed in appellate courts, where the decision may have broader implications beyond the parties involved in the case. The brief typically includes legal and factual arguments, as well as references to relevant authorities and precedents.