Staff Sergeant (SSG) is the title of the E-6 rank in the U.S. Army and United States Marine Corps. It is just above Sergeant. It is just below Sergeant First Class in the U.S. Army or Gunnery Sergeant for the Marine Corps. It is a non-commissioned officer.
In the United States Air Force a Staff Sergeant (SSgt) is the title of an E-5. It ranks just above Senior Airman (SrA) and below Technical Sergeant (TSgt). It is the Air Force's first non-commissioned officer (NCO) rank.