Final answer:
The 'tenth justice' refers to the Solicitor General of the United States, who has significant influence over which cases the federal government appeals to the Supreme Court, as his or her approval is required for such appeals.
Step-by-step explanation:
The term “tenth justice” is often used to refer to the Solicitor General of the United States. This is because the Solicitor General plays a crucial role in determining which cases the federal government will appeal to the Supreme Court.
The Solicitor General must approve any case in which the government is appealing a decision before it can proceed to the Supreme Court, effectively giving him or her significant influence over the Court's docket.
The Supreme Court usually follows the recommendations of the Solicitor General regarding which cases to hear, as the Solicitor General is responsible for representing the federal government before the Court.
This gives the office of the Solicitor General considerable sway in the judicial system, especially since the Supreme Court Justices, who serve lifetime terms, look to the Solicitor General for guidance on matters involving the federal government.
Additionally, in some instances, the Supreme Court may request the Solicitor General's opinion even when the United States is not a direct party to a case, further illustrating the significant influence of this role.
Consequently, this unique position within the U.S. legal system has led to the Solicitor General being informally anointed as the 'tenth justice.'