Latin for "friend of the court." It is advice formally offered to the court in a brief filed by an entity interested in, but not a party to, the case.
A party that is not involved in a particular litigation but that is allowed by the court to advise it on a matter of law directly affecting the litigation.
Duhaime Legal Dictionary
A person, lawyer or not, asking for permission to speak to the Court in a case in which they are neither plaintiff or defendant, usually to point out a notorious fact not known to the Court (such as the sudden death of a party) or a point of law or recent change in the law or a law case on point not apparently known to the Court.
(Latin: “friend of the court”), one who assists the court by furnishing information or advice regarding questions of law or fact. He is not a party to a lawsuit and thus differs from an intervenor, who has a direct interest in the outcome of the lawsuit and is therefore permitted to participate as a party to the suit.
An amicus curiae normally may not participate except by leave of the court, and most courts seldom permit persons to appear in such a capacity. The Supreme Court of the United States, however, permits federal, state, and local governments to submit their views in any case that concerns them without obtaining the consent of either the court or the parties. Private persons may appear as amici curiae in the Supreme Court, either if both parties consent or if the court grants permission.
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.
One (as a professional person or organization) that is not a party to a particular litigation but that is permitted by the court to advise it in respect to some matter of law that directly affects the case in question.
The Free (Legal) Dictionary
Literally, friend of the court. A person with strong interest in or views on the subject matter of an action, but not a party to the action, may petition the court for permission to file a brief, ostensibly on behalf of a party but actually to suggest a rationale consistent with its own views. Such amicus curiae briefs are commonly filed in appeals concerning matters of a broad public interest; e.g., civil rights cases. They may be filed by private persons or the government. In appeals to the U.S. courts of appeals, an amicus brief may be filed only if accompanied by written consent of all parties, or by leave of court granted on motion or at the request of the court, except that consent or leave shall not be required when the brief is presented by the United States or an officer or agency thereof.
An amicus curiae educates the court on points of law that are in doubt, gathers or organizes information, or raises awareness about some aspect of the case that the court might otherwise miss. The person is usually, but not necessarily, an attorney, and is usually not paid for her or his expertise. An amicus curiae must not be a party to the case, nor an attorney in the case, but must have some knowledge or perspective that makes her or his views valuable to the court.
Amicus curiae or amicus curi (plural amici curiae) is a legal Latin phrase, literally translated as "friend of the court", that refers to someone, not a party to a case, who volunteers to offer information on a point of law or some other aspect of the case to assist the court in deciding a matter before it. The information may be a legal opinion in the form of a brief, a testimony that has not been solicited by any of the parties, or a learned treatise on a matter that bears on the case. The decision whether to admit the information lies with the discretion of the court.