The phrase "defense secretary" refers to the head of the United States Department of Defense. Other synonyms that can be used to describe this position include Secretary of Defense, Defense Minister, Minister of Defense, Secretary of War, and even Chief of Staff. These titles are used interchangeably in various countries around the world where the defense secretary is a government official who is responsible for national security. The primary role of a defense secretary is to formulate and implement defense policies for their respective countries, while ensuring that their armed forces maintain the necessary level of readiness to defend their country and its interests.