Final answer:
An amicus curiae brief is a legal document filed by a non-party group to influence a court's decision on a case it is interested in. It educates the court on the potential impact of a ruling and allows interest groups to lobby the judiciary.
Step-by-step explanation:
An amicus curiae brief, also known as a 'friend of the court' brief, is a written document in which a group that is not a party to a legal dispute explains to a court its position on the matter being handled by the court. This is significant as it allows interest groups to present legal arguments stating why the court should rule in a certain way, influencing the judiciary without being a direct party to the case. When the Supreme Court or any other court agrees to hear a case, they allow parties with substantial interest in the outcome to submit amicus curiae briefs to express their views and potentially affect the court's decision. For example, in key cases like Obergefell v. Hodges, numerous interest groups filed amicus briefs to convey their stance on the issues at hand.