Original: The Chief Justice of the United States is the head of the United States federal court system (the judicial branch of the federal government of the United States) and the chief judge of the Supreme Court of the United States. The Chief Justice is one of nine Supreme Court justices; the other eight are the Associate Justices of the Supreme Court of the United States.
Simplified: The Chief Justice of the United States is the senior judge of the Supreme Court of the United States.