An amicus brief, or 'friend of the court' brief, is a legal document filed in court by non-litigants with a strong interest in the subject matter of a case. This document aims to provide additional information, insights, or perspectives that the court may find valuable when making its decision. Amicus briefs can influence the selection of cases and impact the Supreme Court's rulings, as they often represent various interest groups, organizations, or experts with relevant expertise.