A tier is the level of court in the Triumvirate. There are three levels although there is only one court in the Triumvirate: the Supreme Court. A court can overrule the ruling or decision of a court in a lower tier than it is in.
The tier designed almost exclusively for appeals from the first tier. The only court in the second tier is the Court of Appeals which is an intermediary court between the lower courts and the Supreme Court.
The Supreme Court, being the highest court in the Triumvirate, is the only court in this tier. It can overrule any court below it and is considered by many to be one of the most powerful institutions in the Triumvirate political system.