What is Cadet?

Legal Definition
A cadet is a trainee. The term is frequently used to refer to those training to become an officer in the military, often a person who is a junior trainee. Its meaning may vary between countries. The term is also used in civilian contexts and as a general attributive, for example in its original sense of a branch of a ruling house which is not currently in the direct line of succession.
-- Wikipedia
Legal Definition
In the United States laws, students in the military academy at West Point are styled "cadets;" students in the naval academy at Annapolis, "cadet midshipmen." Rev. St. ยงยง 1309, 1512 (U. S. Co.mp. St. 1901, pp. 927, 1042). In England. The younger son of a gentleman; particularly applied to a volimteer in the army, waiting for some post. Jacehi
-- Black's Law Dictionary
Legal Definition
A younger brother, one trained up for the army or navy.
-- Bouviers Law Dictionary