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.

A non-commissioned officer (NCO) is a military officer who does not hold a commission. Non-commissioned officers usually earn their position of authority by promotion through the enlisted ranks. In contrast, commissioned officers usually enter directly from a military academy, officer training corps (OTC) or reserve officer training corps (ROTC), or officer candidate school (OCS) or officer training school (OTS), after receiving a post-secondary degree.