A drill instructor is a non-commissioned officer in the armed forces, fire department, or police forces with specific duties that vary by country. Foot drill, military step, and marching are typically taught by drill instructors.

Sergeant (Sgt) is a rank in use by the armed forces of many countries. It is also a police rank in some police services. The alternative spelling, serjeant, is used in The Rifles and other units that draw their heritage from the British light infantry. Its origin is the Latin serviens, 'one who serves', through the Old French term serjant.