The United States Secretary of Defense is the head of the Department of Defense, responsible for coordinating and overseeing all agencies and functions related to national security and military affairs. This position is a key member of the President's Cabinet and serves as the principal defense policy advisor to the President of the United States. The Secretary of Defense is appointed by the President and must be confirmed by the Senate. This role involves managing the armed forces, formulating defense policies, and ensuring the readiness of military operations. The Secretary also plays a crucial role in international relations and defense strategy.