Amicus Curiae literally translated from Latin is "friend of the court." Plural is "amici curiae."
Generally, it is referencing a person or group who is not a party to an action, but has a strong interest in the matter. This person or group will petition the court for permission to submit a brief in the action intending to influence the court’s decision. Such briefs are called "amicus briefs."
[Last updated in June of 2022 by the Wex Definitions Team]