Final answer:
An amicus curiae brief is filed by someone not directly involved in a case, commonly by interest groups, to present opinions and recommendations to the court.
Step-by-step explanation:
When a party not directly involved in a court case files a brief supporting one side or the other, it is called an amicus curiae brief. This term translates to "friend of the court," and such briefs provide opinions, analysis, and recommendations for how the Court should rule on a certain case.
These documents are especially common when interest groups wish to influence the judiciary by expressing how the court's decision may impact the public or specific populations. These amicus curiae briefs are often filed with permission of the Court, and they play an integral role in showcasing perspectives beyond those directly tied to the case.