Cadet derives through the identical French from the Late Latin capitettum, a diminutive of caput, head, through the Provencal form capdet. It first meant the head of an inferior branch of a family, a younger son; then particularly a military term for an accepted candidate for a commission in the army or navy, who is undergoing training to become an officer- the latter use of the term arose in France, where it was applied to the younger sons of the noblesse who (another 'fitting' alternative was an ecclesiastical benefice) gained commissioned rank, not by serving in the ranks or by entering the écoles militaires, but by becoming attached to corps without pay but with certain privileges.

Military context

Also see: Officer Cadet

In Australia, a "Cadet" is a person aged between 13 and 20 who is a member of the Australian Defence Force Cadets (ADFC). The ADFC is comprised of the Australian Navy Cadets (ANC), the Australian Army Cadets (AAC), and the Australian Air Force Cadets (AAFC).

In Canada, the term "cadet" refers to either an officer in training, with the official rank names as Officer Cadet for the Air Force and Army and Naval Cadet for the Navy. Also, the term Cadet can relate to the subdepartment of the Department of National Defence (DND), the Cadets Canada movement. This consists of Sea Cadets, Army Cadets and Air Cadets in units across Canada.

In Commonwealth countries, including United Kingdom, a cadet is a member of one of the cadet forces.

In Germany, the rank Cadet (German: Seekadett) only exists in the German Navy for officers in training. In the Army and the Luftwaffe, officers in training usually have the rank of a Fahnenjunker or Ensign (German: Fähnrich) before they are promoted into the rank of a Lieutenant.

In Ireland, Cadet is a pupil of the Military College, which carries out officer training for the Air Corps, Army and Naval Service. Training takes 2 years and the Cadets are split into Senior and Junior Grades and Classes.

In Norway, "cadet" is a pupil of the "Krigsskolen", of the schools of either the Army, the Navy, or to the Air Force educating commanding officers. Today the nco's unfortunately hold their ranks at the Military Academy.

In the United Kingdom cadets are: the Combined Cadet Force, the Sea Cadets, Army Cadets and the Air Training Corps.

In the United States, cadet refers to an officer in training. Students at the United States Military Academy, the United States Air Force Academy, and the United States Coast Guard Academy are referred to as "cadets" and members of the Reserve Officers' Training Corps and the Junior Reserve Officers' Training Corps programs of the same uniformed services are also referred to as cadets.